Theoretically you can eliminate metaphor, yes, but you are working against human nature itself.

Certain metaphors are exceedingly common and embedded in the very grammar of many languages (although their exact expression may vary), so in that regard, avoiding metaphor is extremely difficult because it's somewhat an inherent part of the human psyche. Either you will subconsciously integrate some of it, or your users will inevitably create some. Grammaticalization typically originates directly in widespread metaphor.

Your etymologies and extended meanings (because even in an auxlang, creating a root for every meaning is downright exhausting: there's a reason most auxlangs borrow at least part of their vocabulary!) are usually going to be metaphorical in some ways, whether from real languages or from otehr roots. Indeed, "metaphor" is an example: etymologically, the meaning is "carry over, transfer".

Examples

Up is good, down is bad, quality is possession (hence the use of "have" for qualities and actions), individuals are samples ("a human has two eyes" is metaphor: you don't mean a specific human!).

Time is a major source of metaphor in this regard. Time usually moves from back to front. Movement is the key word: verbs of movements are extremely common expressors of time relations!

The body is space: using body parts to generate locatives is also a very common feature cross-linguistically, found in languages as distinct as Hebrew, Nahuatl and Swahili. The fact that virtually all languages in the world use body-relative directional (in front of, behind)... except for the aboriginal language Guugu Yimithirr, well known for using only absolute directions.

Fabrication is causation: the use of verbs meaning "make, create, fabricate" as causative auxiliary is a common metaphoric transfer of the idea of creating an object to "creating" an action in something else.


Does Dovahzul have the same grammar rules as English, or are they different?

There are a lot of rules that are exactly the same.  For instance, Dovahzul has the exact same parts of speech:

Nouns
Verbs
Adjectives
Adverbs
Articles
Conjunctions
Interjections
Prepositions

However, there are some rules that are different: for instance, in the Dragon Language, some words can be used either as an adjective, noun, verb, or adverb, such as the word Nahlot, which means officially "Silenced," but whose meaning can be expanded to mean "silent," "silently," or "silence."

So yes, it shares some rules with English, but no, its rules are not the same.  If you had any specific questions about specific rules, you'd have to ask those in separate questions.


Alternatives to independent verbs for encoding desiderative meaning

Quite a few languages have desiderative as an affix within the verbal system (whether it is analysed as an affix or a full mood being irrelevant here). Japanese and Sanskrit do, for example. It is fairly common (as one would expect) for agglutinating or polysynthetic languages to have one such as Quechua, Finno-Ugric or Turkic languages. It is by no mean universal for these languages: while Hungarian has such a suffix Finnish (and I believe Estonian) lacks it.
Desiderative construction otherwise tend (again not unexpectedly) to be mediated via an auxiliary verb (in Nahuatl, that verb is one of a couple that can be directly integrated into other verbs).
Note that desiderative applies (typically) only to the subject. That is, a form like "I want X to Y" is not a desiderative per se. More accurately, in most language with derivational desiderative affixes, these affixes do not have a "separate" argument structure the way an auxiliary verb an have, so they cannot insert an additional argument. Indeed in Nahuatl, that is exactly what you'll see:

Ticchīhuaznequi (You want to do it)
Ticnequi nicchīhuaz (You want me to do it)

I have not found an easy way to search for information about the three-argument version ("I want X to Y") cross-linguistically, but I'd wager it tends to be formed with some form of Optative or Subjunctive structure.


Is there any concept of "isomorphic" constructed languages?

There is the term relexification meaning that the words of a given language are replaced by new words without changing the structure of the starting language. Relexification does not only occur in conlangs but also in natural languages.


Which sounds could a lipless humanoid produce?

At first sight, it seems that it is impossible for the lipless humanoids to produce any sounds that involve the lips in their production, this concerns the following groups of sounds:

bilabial consonants: pʰ p p' b m w
labiodental consonants: f v
labialised consonants: qʷ χʷ
rounded vowels: o u ɔ

But: There is a known art, named ventriloquism, where replacement sounds for those sounds that require visible lip movement are used to produce understandable speech. Maybe the lipless humanoids can cope with this and even learn to produce the Gé̃kt's sounds using such techniques.


Dealing with core argument loss from syntactic applicativization

I don't think there are any attested languages that limit the role that relative clause heads can have in the matrix clause. The accessibility hierarchy is a theory explaining the capabilities of various languages to produce relative clauses where the head has specific roles in the relative clause.

If we take your example and exchange  the matrix and embedded clauses, you get the following examples. I'm changing the first example also to use a resumptive pronoun.

1a)  *The telescope that I see Bill with it is on the hill.

2a)   The telescope that I see-app is on the hill.

If you want to reintroduce the demoted argument Bill, you can use an adposition or a case. Suppose you reuse the preposition towards for this purpose.

2b)   The telescope that I see-app towards Bill is on the hill.

One interesting choice would be to use neither cases nor adpositions.

2c)    The telescope that I see-app Bill is on the hill.

Since the embedded clause already has a subject and obliques can't be relativized, that forces the interpretation of Bill as an oblique.


What significant traits are found in conlangs and not in natlangs?

There are a broad range of answers possible here and it would be impossible to list everything. In general, it is rather easy to come up with a feature that does not seem to occur in natural languages: simply take a feature every language appears to possess (for example: phonemes, verbs, hierarchical syntax that can be described with syntax trees, a very large amount of words) and reject it. Then see what you can do with the language. This leads to so-called Engelangs, short for “Engineered Languages”.

Alternatively, one can from the ground up decide to build structure from a different “philosophy”, e.g. build on predicate logic, or stacks (the CS concept), or… well, whatever you can think of that can organize information, really.

To make an example, there is Ithkuil. Ithkuil does not strive to be a naturalistic language. Instead, its goal is to allow for unambiguity. Among the things it does to provide that are a range of grammatical inflections not found in any natural language - too many to list, but one example I can make is its case system. In most natural languages, case is something of a helper to syntax. Case marks words for their syntactic roles and thus helps create the structure necessary to understand a sentence. In Ithkuil however, case marks semantics. The sentence “I hit you” in ithkuil would require different cases for “I” and “you” depending on whether e.g. I was a volitional actor, or whether the hitting was an unavoidable circumstance, or an accident, or mediated by someone else… While traces of such systems are found in natural language, none get even close to the extreme of Ithkuil.

Finally, an interesting anecdote is the Conlang Trigger System, a novel way of structuring languages employed in naturalistic conlangs (i.e. ones striving to be mistakable for natural languages). The trigger system developed from misunderstandings of the way certain Austronesian languages (such as Tagalog) work. It’s a perfectly plausible system… just not actually attested in natural languages. I believe there’s a nice writeup on the whole topic, but cannot find it right now.


Four vowels, with no /i/ sound. Is it possible?

This would be very unstable in a human language. For an example of what happens when this vowel is missing, let's look at English's Great Vowel Shift. One of the first things to change was /i:/ becoming /aj/, leaving it without /i/. Within less than a hundred years, /e:/ had migrated to take its place.

In your specific case, I would expect /e/ -> /i/, /a/ -> /e/, and /o/ -> /ɒ/ in fairly short order.

This is because vowels like to spread out on the vowel chart and become more distinct to improve understanding. Because of the limitations of your mouth making it difficult to have highly fronted low vowels, the general rule is that you will have more high vowels than mid or low vowels. Your vowel system violates this universal (with more mid vowels than high vowels).


You could just list them under the stem in that case. If you can easily reconstruct the infinitive by a simple rule, then that would be the easiest way. There is no law that states that you always have to put the infinitive as the main dictionary entry. It's only common practice in most Western languages because it suits the way they work.
Another possibility would be to look at how other languages deal with this issue. For example, Indonesian verbs also tend to have prefixes; I'm not sure what they do in the dictionary. In Arabic, I believe the root is in the dictionary, ie the three core consonants from which the other forms are derived.
Just do whatever works for you: it's your language after all!


Organizing a lexicon in a logographic writing system

Having a dictionary ordered by theme or idea is a good thing and it can carry you a long way in the design of your writing system.

For a more systematic approach, you need a way to order your logograms. Chinese sorting may be an inspiration for you. They identify a "radical" in each character, and than order by radical + number and order of additional strokes. The approach has the advantage that simpler characters (with fewer strokes, and probably more frequent usage) come before more complex ones.


Name of a group of languages with has "less is more" property

These languages could be called minimalist conlangs. This term has been applied to languages like Toki Pona quite regularly, as a Google search will bear out. The term has also been used to describe a number of languages on the CBB, such as Sint and Nomadic.

The same word can be applied to parts of a language, e.g. Davush on CBB refers to their Shiruitoan language as having a minimalist phonology.


Are there any constructed languages designed for legal agreements / country constitutions?

It strikes me that, while this is not precisely what you're asking, Law French I think it might be argued fits the bill.

While French, of course, was the everyday language of the upper class in England from the mid-11th to the late 14th century, and was therefore naturally the language of the Law, it can hardly be called a "constructed language". But after this time, it might be said that, divorced of all real connexion with French or Anglo-French culture, Law French came to be something like an invented language based on natural French. It was certainly a group project (lawyers and judges, all others need not apply).

Later examples are both humorous and instructive:

Richardson Chief Justice de Common Banc al assises de Salisbury in Summer 1631 fuit assault per prisoner la condemne pur felony, que puis son condemnation ject un brickbat a le dit justice, que narrowly mist, et pur ceo immediately fuit indictment drawn per Noy envers le prisoner et son dexter manus ampute et fix al gibbet, sur que luy mesme immediatement hange in presence de Court.  -- Sir George Treby

ahem

Perhaps Law French might best be called a deconstructed language?

About all that's left in modern times are a few set phrases, mostly in Parliament:

La reyne (or le roy) remercie ses bons sujets, accepte leur benevolence, et ainsi le veult -- (The Queen/King thanks her/his good subjects, accepts their bounty, and wills it so)
La reyne (or le roy) le veult -- (The Queen/King wills it)
La reyne (or le roy) s'avisera -- (The Queen/King will advise)
Soit fait comme il est désiré -- (Let it be done as it is desired)

Even in the USA, we still hear oyez, oyez, oyez when court comes to order.

Some interesting notes on Law French, especially pertinent to the question:

"The effort of reporting English speech in French was not merely an expression of affection for the past, for in the long run it probably saved a lawyer more time and trouble than was taken to learn it. ... The formalised French phrases used in the year books gave him a shorthand ready made and adapted for legal purposes."

"To the linguist, Law French is a corrupt dialect by definition. Anglo-French was in steady decline after 1300. ... (That English lawyers could seriously complain that French, spoken in France, had deteriorated considerably as compared to its use in England) is in itself a clear demonstration that by the middle of the fifteenth century there was a marked difference between the French of English lawyers and the French of France."

A Frenchman living in England during Elizabeth I's reign noted of Law French "...now it seemeth that almost there is no language more far from the true French, then the French of our lawes: There being almost no word, which either by intermingling, or adding, or diminishing, or changing of a letter into another, they have not altered and corrupted."

"The lawyers also took what seemed to be a perverse delight in pronouncing Law French as if it were English: indeed, 'their pronunciation differeth so much from ours (French) as it is impossible for a Frenchman to understand them'.

"Few of those who used French paid the slightest attention to grammar or vocabulary."

All taken from J.H. Baker's Manual of Law French


Probably the best technique is making the language weird by absence. Instead of giving the language weird phonemes, make it lack the most common phonemes. A language with 5 vowels but no /a/, /i/ or /u/. A language with several consonants, but no /p/, /t/, or /k/. Or totally without bilabials. Or with no stops.


What is the meaning of this Toki Pona sentence?

I finally got an answer from the author. The sentence meant:

pona sona pi (wawa pi ma Lipija) poka toki lawa mute pi jan lawa nanpa tu pi ma Atilanisi.
The influence of Libyan power on the election of Atlantis' vice president.

The closest translation was "The strength of Libya beside many commands of vice president of Atlantis" by jastako.
Here's a word-for-word translation for what I understand.

pona sona was in fact pana sona: influence (idea sending)
wawa pi ma Lipija: Libyan power
poka: on, about
toki lawa mute: elections
jan lawa nanpa tu: vice president
ma Atilanisi: Atlantis

Suggestions
Feel free to explain how you would have translated that phrase into toki pona.
John Clifford's (Facebook)

kama pi wawa pi ma Lipija pi wile pi jan mute pi jan lawa nanpa tu pi ma Alansi.

Mine

pana nasin pi wawa pi ma Lipija tawa wile kulupu pi jan lawa nanpa tu pi ma Alansi.


Languages where the part of speech of a root is "fixed"?

This is pretty common in natural languages. Think about English words -- most of them have an inherent part of speech and require derivational affixes to change that. "Anger" is inherently a noun and requires "-y" to become an adjective, whereas "excite" is inherently a verb and requires "-ment" to become a noun or "-ed" or "-ing" to become an adjective. This sort of thing is incredibly normal in natlangs -- the reason it seems a bit abnormal in Esperanto is that Esperanto derivation is far more productive than even derivation-heavy natlangs, leading to irregularities in these sorts of changes being much more noticeable.

Also, as an aside, because "human-" is inherently adjectival, you would not say "humano" to mean "humane-ness", but "humaneco" (source). Adding the "-eco" suffix, meaning "the quality of" or something to that effect, is necessary for adjectival Esperanto roots. This is the very reason why Esperanto roots are said to have inherent part of speech, and it's a large part of why the "-eco" suffix exists in the first place.


Do we know languages which think about subordinate conjunctions (like 'as,' 'even,' 'while') differently than English does?

In Inuit languages, there are no separate subordinating conjunctions. In Inuktitut, you identify the subordinate clause by an affix that indicates a conjunction.
For example, take the sentence "While Mary was eating, John was walking." In some Inuktitut dialects, you'd only indicate time tense for the superordinate phrase ("John was walking"), while the subordinate verb wouldn't have a tense marker, but instead use the conjunctive affix -tillu- (with the appropriate person marker)

Mary niri-tillugu John pisu-lauq-tuq (Mary eat-CONJ.3s John walk-Past-Part.3s)

It obviously gets a lot more complicated, but that gives one example of how to do it. If English had a similar setup, you might see something like this:

Mary eat John walked.

If, on the other hand, you wanted to relate them serially (Mary ate then John walked), you might see this sort of construction:

Mary ate John walked.

And you'd obviously reverse them for the other sequence, so "John walked Mary ate."
Obviously it would have to get more sophisticated, but you get the idea.


Next project: Pama-Nyungan inspired vocabulary, but using English words


Are words for "machine" and the like in Tolkien present in Elvish/Westron?

Quenya has tanwë which means "device, craft, construction."  A search for "machine" on this site which may or may not be reputable gives a couple of other words in Quenya, Sindarin, and Noldorin.

Tolkien did once use the word gun in the Hobbit.  This question on sff explains that, and the top answer to it includes this quote:

  The Common Speech, as the language of the Hobbits and their narratives, has inevitably been turned into modern English. In the process the difference between the varieties observable in the use of the Westron has been lessened. Some attempt has been made to represent these varieties by variations in the kind of English used ... (LOTR: The Return of the King, Appendix F, "II. On Translation")

I'd recommend reading the entire answer.

Anyway, it seems that, logically, there should be no words for "future" technologies in Middle earth; any translation of them by Tolkien can be explained as Tolkien trying to make it easier for us to understand.

The other point I want to bring up is that many of the words found in modern Quenya dictionaries are not original creations by Tolkien, but derivations from his notes.  I doubt he created these words intentionally to violate the technology level of the world.

In the Black Speech, we have only a very limited number of words, as seen here; in Dwarvish, as you pointed out in your own answer here, Tolkien has a very limited vocabulary, and only one word has been borrowed from Khuzdul into the Elvish languages.

I think the quote you have about Sauron being a robot is not literal--the orcs' tehnology was no more advanced than the men and the elves'.  I'm sure that "mind of metal and wheels" is meant to be some Entish idiom that references being hasty.


How could my to be constructed language reflect a culture of carefulness?

My idea on that would be very close to what you suggested yourself: introducing suffixes / prefixes which would indicate the uncertainty of the word.  For instance, let's suppose that your word for "strong" is hariq, your word for "I sit down" is brumo and your word for "house" is niptug, and the word for "in" or "inside" would be bomp.*

Now I would invent some prefixes, such as ar- meaning "with great certainty," no prefix meaning something along the lines of "a certain degree of certitude, but not absolute certainty," (such as, it is supposed that; it is presumed that) and fun, meaning, "a large amount of uncertainty" (such as "we think" or "it appears possible that")**

Now let us suppose that I want to say that I that I sit down in the house, with an extreme certainty that it was a house that I was sitting in, but the fact that I was sitting or that I am actually inside is assumed to be true, though it could be theoretically disproved.  I would say,

arniptug bomp brumo

In this fictive language,

funhariq niptug arbomp brumo

would mean, "I sit down in a place definitely inside a house which appears to be strong."

Note that these suffixes / prefixes could theoretically be added to any part of speech, or made different for nouns, verbs, adjectives, interjections, etc.

You could also possibly devise a way to make the order of the words show a carefulness about exactly how accurate what is being said is.

* Words invented totally randomly.
** Again, randomly selected; more or less prefixes could be used,
 with different definitions.  This is just an example.


Are there human beatbox inspired conlangs?

I tried to find conlangs based on such sounds but could not find any. However, the closest human phonemes to such sounds are clicks and many conlangs use them. I don't know any well-known conlangs that use clicks, but HyPry and Gdili were two that I could find.

You could try making one yourself, but given that Beatbox sounds are fairly limited and sometimes hard to distinguish, I doubt you would be able to make an effective language from it without adding in typical consonants and vowels.


Have language regulators ever made concessions and changed the language to adopt naturally occurring changes?

It would seem that Esperanto is one such that not only has done so, but actually has an Academy to guide and legitimize the process.
This article makes note of several, such as new ungendered pronouns (ŝli < ŝi au li; ri = they s.) and the degendering of formerly masculine nouns (dentisto =/= male dentist).
I'm sure that these proposals are coming from the community of speakers themselves and are being agreed to by consensus before any kind of official blessing.


This is only an answer to the first part of the question

I was curious if anyone has ever made a image language?

Yes, there are such languages. They are called pasigraphy or logographic writing system, and the most successful among them is Bliss symbolics (also known as Semantography) by Charles K. Bliss.
I am not aware of automated translation tools or other tools helping in creating pasigraphies.


The phonology table shows it quite simply, it modifies the e to indicate that it is a long vowel. I don't know why the vowel table shows the dipthongs a:i and a:u but not e:i (or any others).

Note that although this may seem to be a common colon, the actual IPA diacritic is two triangles, flat sides on the outside: U+02D0 ː. But as the colon doesn't have another meaning in the IPA and it's much easier to type, a lot of people just use it instead.


How long do I need to influence language development?

Assuming emperor Kai puts a strong pressure on his subjects, having the change permanent would be a matter of one or two generations. Once one generation is brainwashed and use naturally the new form, and that there is no backward trend (emperor Kai's death penalty may be a strong incentive to avoid such trend), consider that adoption should stay.

This however assumes that language is mostly spoken and not written (or you need to change writings as well), that teachers are supportive of Kai and teach the new proper way of speaking to all, etc.


Conlangs based on lesser known antique languages

Eressilian (Hittite)
I wrote the answer you linked, which talks about Eressilian, a conlang based on the Hittite language, supplemented with loanwords from Arabic, ancient Greek and Persian. I talked there about the Greek influence (which is slight, from the information we have); the Hittite roots are of course much stronger. An example passage given by the creator shows Article 1 of the Universal Declaration of Human Rights, in Hittite and Eressilian:

Hittite
Hūmant+es antuhsa+es arawa+iya+ya annual+iya kraht(Persian)+a hoquq(Persian/Arabic) anda asanzi hassant+ke. Anda mem+iyan+a wajidan(Persian) asanzi har+ke+ya  ēsdu aniya+du adelphotés(Greek)+us katta hūmant+as anda.
Eressilian
Uvẽndesh ãndushesh irawedhadha ãnnuelidha krata ukuk ãnda eshẽnji eshshẽndke. Ãnda mẽvedheva wajidan eshẽnji erkedha ishchu enidhadhu elelpulush kata uvẽndesh ãnda.

I don't have a grasp on the pronunciation of either language, but after attempting to sound it out, the two are quite similar. For instance, the Hittite "antuhsa es" appears similar to the Eressilian "ãndushesh" - both meaning, I believe, "man" or "human".
Goa'uld (Egyptian) (sort of)
This is the "language" spoken by the Goa'uld race in Stargate. It's ostensibly based in ancient Egyptian, drawing from the language and hieroglyphs - appropriate, given that the Goa'uld supposedly ruled Earth as gods, sometimes appearing as the gods of the ancient Egyptians. I keep seeing references to a writing variation called Nakht, which I can't find much information on.
Some (though not much) of the writing uses the Meroitic system. To my (untrained) eye, there don't appear to be a huge amount of similarities (see Meroitic and Goa'uld), but some crossovers show through pretty easily, such as "l"s and "n"s. Those are probably the main Meroitic contributions.
All that said . . . Goa'uld vocabulary is basically made up, and so it's not really a conlang. No attempts were made to keep much linguistic continuity, and so it's not a constructed language as such. There are probably some similarities to ancient Egyptian, but likely not many. I include it here only because its use of some ancient Egyptian hieroglyphs is notable; it appears that an alphabet for the language was indeed constructed.
Irǧeret (Egyptian and Akkadian, with Ugaritic, Arabic and Hebrew influences)
This one seems decently documented by its author. The vocabulary and phonology are derived from Egyptian, although there isn't much vocabulary listed. The organization of nouns - in number and gender - resembles Akkadian. It also contains the Akkadian declensions, with the addition of the dative. In short, the grammar and morphology appears Akkadian, while the vocabulary should be Egyptian. It's an interesting blend.
A note on Proto-Indo-European
A couple of languages have been derived from Proto-Indo-European, the reconstructed common ancestor of Indo-European languages. It's only known indirectly. Therefore, many (though not all) conlangs that are based on it also use words from more recent Indo-European languages. Proto-Indo-European is certainly antique; whether it's "lesser-known" is perhaps another question entirely. That said, it's not a terribly common template, and so I'm listing some Proto-Indo-European languages here for the sake of interest.

Sambahsa:  Sambahsa, an international auxiliary language, appears to be heavily influenced by Proto-Indo-European, primarily through vocabulary. It modifies words from languages ranging from India to Spain, attempting to go back to the languages' common roots.
Atlantean (Proto-Indo-European): Like Sambahsa, Atlantean is Proto-Indo-European in origin, especially when it comes to vocabulary (grammatically, it is quite different). Notably, it was created by Marc Okrand, the man behind Klingon. According to the linked website, Okrand

took Proto-Indo-European roots and then compared them with language families at various points in time from around the world.  Where similarities between words existed, he altered the root or its semantic value to reflect that similarity.  By the combination of the PIE roots and by the adoption of new roots from these world languages, he created a vocabulary.

Given that these languages borrow vocabulary from many descendants of Proto-Indo-European, you could argue that they're not directly based in it. However, the intentional linguistic diversity within the family - and the attempts to base words on common similarities that are attributable to Proto-Indo-European - do seem to make these conlangs its descendants.


How common is it for the creator of a conlang to be fluent in that conlang?

From personal experience (active member in a large server of avid conlangers) very few people ever learn to speak their own conlangs. Language learning is a very time-intensive progress and there is not much gained from learning a language no one else speaks. The occasional exception tends to be found in group projects, in which sometimes at least to a part “creating by using” is used as a technique, which naturally leads to at least rudimentary command of the language. Some languages have also been developed exclusively by using them, such as Viossa, but this is an exception.

You may also be interested in this talk at LCC6, held by Jim Hopkins in his conlang (with an interpreter, of course).  Summary of the talk:

  In this presentation Jim Hopkins, creator of Itlani, will share his tips and techniques for recording, learning, and living the Language of your Soul. He will discuss the need for finding and ensuring stability in your language’s vocabulary and structure to facilitate easier learning, and how to immerse yourself in your language for mental and emotional engagement, even though you aren’t living full time among native speakers. The presentation will be done entirely in the Itlani language, with interpretation into English by Tony Harris.


In what ways are grammatical genders useful?

The generic term for genders is "word classes". In some languages male/female isn't the main way to divide up the world.

Word classes are useful for co-ordination. If a language lacks gender, (or animacy, what have you), then you need some other way to know what adjective goes with what noun, which antecedent a pronoun refers to and so on. A language with lousy coordination might be English, with things like "He saw him hit him with it."

They make languages hard for language learners because the semantic relationship between the word classes overtime becomes increasingly arbitrary and creates a lexical burden for language learners, i.e. you just have to memorize the word class for each word. Also, gender marker is obligatory, so you have a high entry cost-- you can't say anything until you work out the genders of the relevant words.


How can boustrophedon writing systems be published?

Are there any ways of encoding text in Unicode to mark it as boustrophedon?

From the unicode.org FAQ about bi-directional text[1]

  The Unicode Standard does not provide formatting codes to signal boustrophedon text. Specialized word processors for ancient scripts might offer support for this. In the absence of that, fixed texts can be written in boustrophedon by using hard line breaks and directionality overrides.

I don't know of any online method of inputting reflowable boustrophedon text, however there seems to be a LaTeX package[2] availible that offers automation of the process at least in LaTeX documents, both for "regular" boustrophedon and the Rongorongo style where glyphs are rotated rather than mirrored, which would allow for relative ease of publishing pdf documents at leat.


What makes lojban such a "logical" language?

Lojban was designed with a few key features in mind, which are ultimately why it claims the title of "logical" language.

First it's good to know that a logical language actually means something pretty specific. It's usually built on predicate logic, and a desire to express any logically-expressible statement unambiguously. No two statements are allowed to mean the same thing, and no statement is allowed to mean two things.

In this sense, Lojban fulfills the literal criteria for what counts as a logical language. There's also the colloquial sense, though - the way people think about it, when someone says "logical language."

It is designed to be a regular language. This gives it a few key properties that make it easier for computers to process (though it's still an immensely complicated task to implement). Most of these properties are mathematical, and you can read them on the Wikipedia page. However, what it means in an intuitive way is that no word or word phrase's meaning changes based on words it's not adjacent to. That's a nice property when you're a computer and have a hard time maintaining a sense of context.

Lojban also has no irregular forms or rule exceptions whatsoever. All words are constructed based on specific properties that are clearly delineated, using roots that are unique and are intended to mesh with each other as-is.

This means that any construction which can be built in a logical form can be written completely and uniquely in Lojban. There are no ambiguities between forms. Note, though, that this is commonly confused with "the language has no ambiguity." It's possible to be ambiguous in Lojban, but only intentionally, and that ambiguity is unique to the way you wrote it.

It also allows for systematic, structured learning and use. New words fit into the existing grammar and structure without any other prompting, once you know what they mean and how they're used. No additional grammatical structures are needed to use any words, once you know them.


Can features in the physical environment meaningfully affect the development of a local language's phonology?

There has also been evidence that suggests that ejectives tend to occur more frequently in areas of higher elevation, perhaps due to their being easier to produce in these regions:

  We present evidence that the geographic context in which a language is spoken may directly impact its phonological form. We examined the geographic coordinates and elevations of 567 language locations represented in a worldwide phonetic database. Languages with phonemic ejective consonants were found to occur closer to inhabitable regions of high elevation, when contrasted to languages without this class of sounds. In addition, the mean and median elevations of the locations of languages with ejectives were found to be comparatively high. [...] we offer two plausible motivations for [this correlation's] existence. We suggest that ejective sounds might be facilitated at higher elevations due to the associated decrease in ambient air pressure, which reduces the physiological effort required for the compression of air in the pharyngeal cavity–a unique articulatory component of ejective sounds. In addition, we hypothesize that ejective sounds may help to mitigate rates of water vapor loss through exhaled air. [...] Our results reveal the direct influence of a geographic factor on the basic sound inventories of human languages.

(emphasis mine)


How do I naturalistically merge two languages without a clear Substrate and Superstrate?

In fact, there are a lot of possibilities, and many of them are attested in the history of natural languages.

Majority language wins. This happened in China at least twice, it was conquered and ruled by foreign people (Mongolians, Manchu), but the ruling class became sinified. It also happened in medieval France and Spain, they were conquered and ruled be Germanic tribes (Franks and Burgundians for France, Vandals and Goths for Spain), but the majority language of the residents won out.
Most prestigious language wins. This happend in antiquity in the Roman empire, and we see it in many post-colonial states in Africa. There are some prerequisites for that such as a working educational system helping that.
Pidgins and Creoles emerge, and a Creole wins. This can be watched in Papua New Guinea, where Creole languages like Police Motu and Tok Pisin are becoming the de facto standard of communication.
Something else happens. The case of English is not as clear as my points 1.–3. suggest: While the majority language finally won, it was heavily impacted and changed by the languages of the conquerors (Normans and Danes).
EDIT Stable multiliguality. Quite rare in the wild, but Switzerland with a coexistence of Swiss German, French, and Italian is an example. The fourth language of Switzerland, Romansh, is under pressure, despite attempts of language preservation.


Is there any constructed language that eliminated all fallacies related to how language works?

Looking at the list of fallacies you quote, I would say this is not possible — most of them have got nothing to do with the language itself, but with the way it is used. It's a bit like making a kitchen knife that you cannot use to hurt someone with.

The Fallacy of Composition is related to reasoning. I cannot think of any way that a language can make that impossible. As long as you have expressive power in the language to express anything, you can express incorrect reasoning as well. The same goes for False Attribution, which is about how you use language, not anything in the language itself.

Loki's Wager refers to the absence of clear definitions or boundaries. The world is not clear-cut, so language cannot be like that either. Defining where the head starts and the neck ends is unrelated to language. Unless you want to accompany each word in that language with a book that defines exactly what it means.

Even the Fallacy of Accent is a problem, unless you take stress patterns out of the language, which then is a lot less usable, as stress is a good way of expressing nuances of meaning.

Syntactic ambiguity is about the only one which could be avoided through careful language design. But most 'usable' languages have some of that as well, especially if they are reasonably complex.

Most of these verbal fallacies are to do with the way you use language and express meanings, which you could do in any language. Syntactic ambiguities crop up more often than you would think, but unless you are a linguist, you won't even notice most of them, as it is usually very clear which meaning is the appropriate one in the context.

So, my answer is no, because it is not even possible to do that.


Is there any general rule for constructing a word? Example: "q" or "w" should not end a word, something like this

Yes, there are but they are language-specific. These are called phonotactics. They are well explained in the book of David Peterson "The Art of Language Invention"(E-book download link). Actually, these rules include:

structure of a syllable. E.g. in Hawaiian language closed syllables are impossible. So words like "heck" are not allowed. ;)

stress. The Finnish language always stresses the first syllable.

What consonants/vowels can be combined. "st" is quite common in English but not in Hungarian. But "ts" is quite common in Russian but not in English. But on the other hand Russian allows "st" too.

there are many other things. I suggest reading this article on Wikipedia.

P.S. I'm not good at linguistic terms in English, sorry for possible wrong use of words ;)


How would having a logographic writing system work in a conlang?

The problem with pure logographies is that languages tend to have a significant amount of morphemes, be these bound or free, that mark relatively abstract concepts, such as posession, the roles of NPs, etc., and some abstract words are rather hard to draw symbols for. As such, a purely logographic system cannot really deal with natural languages to their full extent, and therefore pick up "impurities", not just out of convenience, but out of necessity, since without them they are generally at best mnemonic aids and not a full (or almost full) representation of the spoken language. If you want a pure logographic system to be realistically viable for your conlang, going the oligomorphemic route, like Toki Pona, is probably the most reasonable, as the low number of morphemes reduces the strain of learning a large number of symbols, as well as the issue of coming up with new ones for new or rarely written-about concepts, since morphemes are a closed class, and the necessarily relatively general meaning of these morphemes means that it would likely be relatively straightforward to represent the majority of them with mostly intuitive iconography.


If you're notating a language that uses [β] or [ɓ] but does not distinguish it from [b], that is, if there are no words such that changing one of these consonants to the other changes the meaning of the word (perhaps because [β] occurs only between vowels and [b] elsewhere), then for most purposes you write them all as /b/; so that is a “simplified IPA”.  This is called broad transcription, written with slashes to distinguish it from narrow transcription using brackets.  A famous example: English /p/ includes both [p] and [pʰ], which are distinguished in many languages including Zulu, Hindustani, Mandarin.
No language makes phonemic distinctions between all pairs of phones represented by distinct symbols in IPA; but every symbol exists because some language contrasts it with others.


Which constructed language has the largest body of literature?

According to magazine author Arika Okrent in "Discouraging Words" from Failure Magazine (July 21, 2009), it's Esperanto.  She writes,

What is the most widely used invented language?
Definitely Esperanto, which is ironic because when you say “Esperanto,” most people say, “Didn’t that die out in the 1920s?” Or, “Esperanto? That failed utopian project?” But in terms of invented languages, it’s the most outlandishly successful invented language ever. It has thousands of speakers—even native speakers—and that’s a major accomplishment as compared to the 900 or so other languages that have no speakers.

That's not hard to believe either.  According to Esperanto.net,

Professor Sidney S. Culbert of the University of Washington, Seattle, USA, has done the most comprehensive survey on language use ever attempted. He has conducted interviews in dozens of countries around the world and tested for "professional proficiency", i.e. much more than just "hello, please, goodbye".
Based on this survey, Prof. Culbert concluded that Esperanto has about two million speakers worldwide.

Obviously, this doesn't quite answer your question, since it was specifically about published literature.  However, according to this answer on the Esperanto stack, there are probably around 200 novels that were originally published in Esperanto, along with 400 volumes of short stories - and that's in the fiction category only.  There's a list of Esperanto libraries on wikapedia, some of which have thousands of works in them.

Very likely Esperanto.


TAKE is Το Ἄνευ Κλίσι Ἑλληνική / Greek Without Inflexions. According to Ray Brown, "Graeca sine flexione" ... (considers) what Greek might be like if stripped of its inflexions in the manner similar to Giuseppe Peano's Latino sine Flexione... It should be pointed out that although Giuseppe Peano produced 'Latino sine flexione' as an international auxiliary language, I am NOT making a similar proposal for ΤΑΚΕ!
Outidic is a kind of IAL for the learned, statesmen & merchants alike.

These are both by Ray Brown of Conlang-L.
Èskova Linga
Engadinese is a Greek-Romansch graftlang.
Atlo Greek appears now to be entirely lost.
Rhaetian

There may be others...


How Standard Average European is Esperanto?

Tl;dr: Esperanto possesses about 8/12 SAE features

Let's go through these features one by one. This is going to be pretty long, sorry for that. For reference, I'm using the famous Haspelmath paper as reference for which features define the SAE sprachbund, as I did in my earlier post.

1. Definite and indefinite articles - ✗

Esperanto defies SAE norms out the gate here, as it only has a definite article.

  libro - "a book"
  la libro - "the book"

This is actually quite bizarre, as those SAE languages that do not fit this criterion (such as Slavic languages, which heavily influenced Esperanto) have no articles at all. However, some neighboring non-SAE languages do have only a definite article, so this isn't too bizarre cross-linguistically.

2. Relative clauses with relative pronouns - ✓

Haspelmath characterizes this way of forming relative clauses, unique to SAE languages, by the following criteria:

The relative clause is post-nominal
There is an inflecting relative pronoun
This pronoun introduces the relative clause
The relative pronoun functions as a resumptive, signalling the head's role in the relative clause.

Esperanto relative clauses fit all of these criteria.

  Tiu blua balono, kion mi estis tenanta, knalis
  "That blue balloon, which I was holding, popped."

Here, the relative clause kion mi estis tenanta follows the nominal head balono. It is introduced by an inflecting relative pronoun kion, which is inflected for the accusative case to mark the balloon's role in the clause (that it is the object of estas tenanta. Pretty much prototypical SAE here.

3. 'Have'-perfect - ✗

Many European languages used a form of "to have" plus a passive participle to mark what we can loosely call the perfect. The languages that possess this construction have grammaticalized it to different degrees, but according to Haspelmath, "what is important here is that they all must have had basically the same meaning when they were first created."

Esperanto does not have a 'have'-perfect. Instead, Esperanto emulates Slavic and Finno-Ugric languages in using "to be" + an active participle -- a form Haspelmath explicitly contrasts with the 'have'-perfect in his article.

  Mi estas vidinta la viron.

mi est-as vid-i-nta          la  vir-on
I  be-PRS see-PERF-ACT.PTCP  the man-ACC

  "I have seen the man."

Unsurprising given Zamenhof's language background, but not SAE.

4. Nominative experiencers - ✓

With "verbs of sensation, emotion, cognition, and perception," there are two main strategies for expressing the experiencer -- either the experiencer is treated like an agent and marked as a nominative subject (e.g., "I like it"), or it is treated like a patient or goal and the stimulus is marked as a nominative subject (e.g., "It pleases me", "It is pleasing to me"). English pretty much exclusively uses nominative experiencers, but this isn't strictly binary across languages -- many languages, including quite a few SAE languages, will have some verbs that do the former and some that do the latter. However, most SAE languages have a very strong tendency to prefer nominative experiencers.

Esperanto primarily uses nominative experiencers.

  Mi vidis fantomon. - "I saw a ghost."
  Mi timas la mallumon. - "I fear the darkness."
  Mi flaras florojn. - "I smell flowers."

Esperanto does possess at least one verb that bucks the trend, plaĉi.

  Ĉokolado plaĉas al mi
  "I like chocolate" (lit., "Chocolate is pleasing to me.")

However, even this construction is gradually becoming less used over time as speakers favor the nominative experiencer verb ŝati instead.

  Mi ŝatas ĉokoladon.
  "I like chocolate."

Therefore, I think it's safe to say that Esperanto is pretty SAE in this regard.

5. Participial passive - ✓

To quote Haspelmath: "Standard Average European languages typically have a canonical passive construction formed with a passive participle plus an intransitive copula-like verb ("be", "become", or the like). In this passive the original direct object becomes the subject and the original subject may be omitted, but it may also be expressed as an adverbial agent phrase."

Esperanto passives behave pretty much exactly in this way. Unsurprising, since none of the language families from which it draws its inspiration differ from the SAE trend here either.

  La knabo estas batita (de sia fratino).

la  knab-o  est-as bat-i-ta           de si-a      frat-in-o
the boy-NOM be-PRS hit-PERF-PASS.PTCP of REFL-POSS brother-FEM-NOM

  "The boy is hit (by his sister)."

Granted, these passive participle constructions in Esperanto can often be avoided using anticausitive morphology or free word order in contexts where this type of passive construction would be unavoidable in, say, English. But this construction exists and is certainly frequently used enough to be considered a nicely SAE feature of Esperanto.

6. Anticausative prominence - ?

Esperanto possesses both a causative affix -ig and an anticausative affix -iĝ, both of which are used very frequently.

fand-i           fand-iĝ-i          brul-i             brul-ig-i
melt-INF         melt-ANTIC-INF     burn-INF           burn-CAUS-INF
"to melt (tr.)"  "to melt (intr.)"  "to burn (intr.)"  "to burn (tr.)"

To say for certain that Esperanto has a preference for one over the other, some proper analysis of the language's vocabulary and usage would have to be done. In my limited experience, I'd say that they're about equally common in Esperanto, but it's really not possible to say without a lot more research into Esperanto verbs and their usage.

7. Dative external possessors - ✓

As @jknappen has pointed out, Esperanto does allow for dative external possessors

  Mi lavas al mi la manoj.
  "I wash my hands." (literally, "I wash to me the hands")

I can't personally speak for how common they are, but the only requirement for this criterion is that they exist.

8. Negative pronouns and lack of verbal negation - ✓

This is another easy one, as this SAE feature is explicitly spelled out in the basic 16 rules of Esperanto:

  When another NEGATIVE word is present, the word NE [English no, not] is omitted.

  Mi ne  venis     Neniu  venis
  I  not come      No.one comes

9. Particles in comparative constructions - ✓

There are quite a few ways of marking comparatives, but particle comparatives like the English "than" are pretty overwhelmingly SAE. Esperanto uses a particle comparative, as its ol is pretty much identical in function to English "that".

10. Relative-based equative constructions - ✓

Esperanto's equative construction tiel ... kiel is actually more transparently based on relative clauses than the English construction, as it uses synchronic relative correlatives -- and even the English "as ... as" construction is considered relative-based by Haspelmath. Another transparently SAE feature.

11. Subject person affixes as strict agreement markers - ✗

It's far more common, cross-linguistically, for languages with person-marking to be pro-drop. However, several SAE languages (including French, German, and English) inflect the verb to agree with the person/number of the subject without allowing the subject to be dropped.

While Esperanto is not pro-drop, to my knowledge, Esperanto does not inflect verbs to agree with the person or number of the subject, and so it avoids this SAE feature.

12. Intensifier-reflexive differentiation - ✓

European languages verb frequently distinguish between intensifiers and reflexive pronouns, but using one form for both appears to be more common worldwide. English actually averts this, as it uses its reflexive in this intensifier function (e.g., "He did it himself").

Esperanto's intensifier particle, mem, is distinct from its reflexive pronoun si.

  Li batis sin.
  "He hit himself."

  Li mem batis ĝin.
  "He hit it himself."

Thus, Esperanto is SAE in this regard.


What is the word “li” in Toki pona, grammatically?

Li in these examples could be described as a copula - this is the name for a word whose function is to link a subject and predicate.


How do Romance-based naturalistic conlangs deal with the different principal parts of a verb?

I answer first for two of my own invented languages, Kerno and Loucarian. Since the question is now broadened to invented IALs, I choose to add several additional sections: Interlingua, Sabir, Occidental, Romanal, Medial Europan and Lingua Franca Nova. Also, just so one can get a flavour of these languages, I append the Pater Noster in each.

Looking back at some of my old Romance languages, I don't think I paid much attention to the Latin principle parts as a system. As the languages evolve out of Latin and into their more modern selves, the systematic nature might fall apart or accrete new forms.

In Kerno, we can certainly see the survival of at least three principal parts for the regular verbs.

cantam, cantar, cantú (sing)
caru, carer, carú (love)
dormu, dormir, dormú (sleep)

It's not until we meet up with those good old irregular verbs that more principal parts seem to linger:

In the Grammar, there is actually a section that lists the principal parts of the irregular verbs (though for some unknown reason, I didn't call them such):

doc (or doy), dar, dedai, doú
istam, ystar, stetai, ystú
currem, currer, coscorrai (or cocorrai), cursú
llodu, lloder, llosès, llosú
ioc, ir, fu, eú
sentu, sentir, senti, sentú

So, four principal parts surviving.

a Phazeoir Nusteor que bias 'n y ceues;
foreth noef il tew nom;
gouenyes il tew camouils;
foreth fès la teva gouoluntáts
en lâ derra cuomo 'ny ceues;
danos-el osdia le nusteor panèn cuotidièn;
dimeti y nusteor dheuz
cuomo dimitemus ai nusteor dheutoeres;
et ne nus attrayer rhen al tentación,
mays eliveránus des val.

Loucarian takes its inspiration from Sabir and has a similarly reduced verbal conjugation.

amare, amando, amato
clevere, cleviendo, cleveto
ajire, ajiendo, ajito
pejeire, pejiendo, pejito
vidure, videndo, viduto

While not a principal part of the ancestral Reman language, modern Loucarian takes the present/infinitive, progressive/continual & past for its principal parts.

nemet sospeito pôdis IC cata maccareire; etti pejeto IC:
enamverver tim maccareire coudeiere ican:
jenì abba en samayam na
qedd al iccà nomon
sôppere al iccà noummen podeqc festinam
outtato wad al iccà alfas eim en al tir eim en al paradeisiam
cvercare tim adis nasser hotim al jenìm pountim cascoumênem
demetere tim al jenìn nobes eim nas demetere al jenìn namaderam
mire doucere nasser adis peirasmom
mire dê côire tim nasser ad injoudissiam.

Interlingua is an invented Romance IAL. From the I-a grammar article under Verbs, we can see exactly what has been done with Latin's principal parts.

All personal inflexion is stripped off, so there can be no "first principal part" as such. However, the Latin present stem remains largely intact, so the I-a present tense could continue to serve as first principal part.
The infinitive remains distinct.
The old Latin perfect stems have all been obliterated; the I-a past tense is formed upon the Latin imperfect (present stem), so there can be no "third principal part".
The Latin past participle remains in I-a.

One could say the principal parts of an Interlingua verb are:

parla, parlar, parlate
dice, dicer, dicíte
senti, sentir, séntite

Interlingua is not entirely regular as regards its verbal system. There are a few (unofficial) irregulars (thank Goodness!)

The principal parts of esser are:

es, esser, era, essite thus four principal parts.

Nostre Patre, qui es in le celos,
que tu nomine sia sanctificate;
que tu regno veni;
que tu voluntate sia facite
super le terra como etiam in le celo.
Da nos hodie nostre pan quotidian,
e pardona a nos nostre debitas
como nos pardona a nostre debitores,
e non duce nos in tentation,
sed libera nos del mal.

Sabir (also knows as Mediterranean Lingua Franca) was an actual, natural Romance IAL in use within the Mediterranean Sea basin from the middle ages onwards to about the mid 19th century or so.

It is well known for severe reduction & levelling of morphology in general. There are but two principal parts, both surviving from Latin:

parlar, parlato
fazer, fazeto
sabir, sabito

The present tense, imperative and infinitive are all wrapped within the immutable infinitive; the past and past participle are wrapped up within the old perfect participle.

There are a couple odd forms. For example, in the Pater Noster we find noi volir ki nomi di ti star saluti of which I (having no grammar of the language available) can only imagine to be a past participle of saluer. Why the -i termination and why not "salueto", I don't know. Obviously Sabir was not designed to level all irregularity. It evolved naturally and over a long period of time within a broad geographical region. Oddities are bound to survive / arise.

Padri di noi, ki star in syelo,
noi volir ki nomi di ti star saluti.
Noi volir ki il paisi di ti star kon noi,
i ki ti lasar ki tuto il populo fazer volo di ti
na tera, syemi syemi ki nel syelo.
Dar noi sempri pani di noi di kada jorno,
i skuzar per noi li kulpa di noi,
syemi syemi ki noi skuzar kwesto populo ki fazer kulpa a noi.
Non lasar noi tenir katibo pensyeri,
ma tradir per noi di malu.

Occidental is another invented Romance IAL. I really don't know much about it beyond a couple articles I've read online. Even so, we can easily pick out the remaining principal parts from a good sample text:

da, dar, dat
inducte, inducter, inductet
veni, venir, venit

As with Interlingua and Sabir, the morphology of person is eliminated, leaving only a present stem. Also, the perfect stem itself is eliminated. This leaves us three principal parts.

Patre nor, qui es in li cieles,
mey tui nómine esser sanctificat,
mey tui regnia venir,
mey tui vole esser fat,
qualmen in li cieles talmen anc sur li terre.
Da nos hodie nor pan omnidial,
e pardona nor débites,
qualmen anc noi pardona nor debitores.
E ne inducte nos in tentation,
ma libera nos de lu mal.

Romanal was another invented Romance IAL. I have again no reference grammar, but a perusal of a text shows some interesting morphology.

das, dar, dat

Forms like ne nos inducas and dimitta speak of the survival of Latin negative imperative and possibly imperative forms as well. Romanal is well worth the visit for the spiffy verbal conjugation alone!

Patro nostri,
qui est en cieles,
sanctificat estas nomine tui,
advenias regne tui,
fias volite tui,
sicut en ciele, et en terre.
Il pane nostri quotidiani das ad nos hodie,
et dimittas nostri debites,
sicut et nus dimitta debitantos nostri,
et ne nos inducas in tentatione,
sed liberas nos ex male.

Medial Europan was another invented Romance IAL.

It would seem, from the given text, that all distinctions of conjugation have been reduced to but one. We can see that the present tense and infinitive are distinct.

pintit, pintir

Un englo, un franco ed un deuto havit le taske pintir kamele. Le englo voyajit ad Afrike for studiir le kamele in tisui doimie. Le franco gidit al zoologi jarden, ed le deuto pintit on kamelo ex le profunde de sui psyke.

Lingua Franca Nova was also inspired by Sabir. Its verbal system is the most reduced respecting the old Latin principal parts. That is to say, there are no principal parts, the bare verb stem being used for all tenses, in conjunction with temporal particles.

leva
come
boli

Nosa Padre ci es en la sielo,
Ta ce tua nom es santida.
Ta ce tua rena veni.
Ta ce tua vole aveni
sur la tera como en la sielo.
Dona oji nosa pan dial a nos,
e pardona nosa detas,
como nos pardona nosa detores,
e no condui nos a tenta,
ma libri nos de malia.

NB: I deliberately left out Esperanto / Ido because, while their vocabulary is largely paneuropean, its grammar is not Romance. (I've read several sources that claim it is closer to Slavic grammatically.) Also, I leave out Novial for the same reason, only its grammar is much closer to that of English.


How do lists of three or more items work in Klingon?

I think it depends on the context. If it is "I can see bears and metal drums", then you would have to repeat the subject and verb, effectively saying "I can see bears and I can see metal drums".

As per The Klingon Dictionary (6.2, Complex Sentences):

  When the subject of both the joined sentences is the same, the English translation may be reduced to a less choppy form, but Klingon does not allow this shortening.

If you are just talking about lists of items without having a complex sentence, then I would think this sentence from 5.3 (Conjunctions) applies (even though it is about the post-verbal meaning of je):

  As in English, the meaning of such sentences is ambiguous: [..] The exact meaning is determined by context.

If there are bears and metal drums, then presumably you're not talking about bears, metal, and drums. An oft-quoted example where there is an ambiguity in English is I am dedicating this work to my parents, the Queen of England and the Archbishop of Canterbury. Without a comma before and, the list could be mistaken for an apposition. Obviously, the context makes this interpretation highly unlikely!

Just remember that language is rarely unambiguous and independent of context; any attempts to avoid this make it very unwieldy. Which is why legal language is typically so hard to read.


Usage of different plural systems in the same language

A similar system to the one you describe is attested in Fijian. Fijian has a single-dual-paucal-plural distinction in its pronouns only. However, almost every sentence must contain a subject pronoun. I'm not sure about the status of imperatives in Fijian. Fijian also has VOS word order, where S is a lexical subject.

Independent nouns themselves are not marked for number and the articles that introduce them are also not marked for number.

era la'o [a gone]
3PL go   DET child
The children are going

In other examples, a gone is glossed as the child. From this we can infer that the subject pronoun (or part of the verb phrase, depending on how you analyze it), is usually the only place in the clause where number is overtly marked. Pronouns can surface in other positions as well, and pronominal number contrasts are not neutralized when the pronoun isn't the subject.

As an interesting wrinkle, pronouns have a separate form that's used when they are the head of a noun phrase, including a subject noun phrase.

era sa  la'o [o   ira]
3PL ASP go   ART  3PL
"They are going"

But, pronouns can occur after the verb without being introduced by an article or a preposition if they are objects.

  o   aa   biu-ti  ira
2SG PAST leave-TR  3PL
"You left them"

More generally, it is somewhat common for pronouns or a subset of the pronouns to have a different number system than independent nouns. Proto-Germanic is reconstructed with dual number in first and second person pronouns and their corresponding verbal forms, but without the dual in the third person or in nouns.


How to classify the language of "Uncleftish Beholding"?

I wouldn’t personally call Anglish (that is, English without non-Germanic (or sometimes even non-Anglosaxon) vocabulary) a conlang. Taken at face value, it replaces English vocabulary 1:1 with coined words, which is basically the definition of a relex. Whether you want to consider relexes a subset of conlangs or an entirely different category (perhaps a subset of ciphers and codes) altogether is subjective.

As a note, Anglish can also just be stylistic in nature — favouring germanic word stems over loaned ones where possible, but in the context of the essay you posted this is clearly not the case.


How do you determine a New Letter's sound?

If you're designing a fully new language, it's usually better to pick phonemes (sounds) before even thinking about orthography. Writing should really come after even grammar.
If you're just designing a new writing system, then yeah, you just make it up.


You're describing a couple different and not totally related things with different terminology used for each:

Classical Latin is an example of a literary language, a language used not really in speech but used to communicate through writing.
Modern Standard Arabic, one of those artificial languages based off of a natural one but not really being a spoken language. It's very frequently affected by diglossia, and not really used in natural settings. It's usually referred to as simply a standardized lanuage, and also qualifies as a literary language.
Hebrew as spoken in daily life in Israel would qualify as the first type you described, a modernized version of an old language that was resurrected after death. It would be referred to as a revived language.


Has anybody created an Arabic inspired shorthand for english?

Do these count?
Anglo-Arabic

Anglo-Arabic, created by Pangus Ho, is a fully phonetic writing system that can be used to write English. It borrows the shape of Arabic letters so that it looks like Arabic at a glance, however few of the letters have the same sound as they do in Arabic. For example the letter "nūn", which is used to symbolize the sound /n/ in Arabic, is pronounced /t/ in Anglo-Arabic. The main objective is to make similar consonants have similar letter shapes. Consonants, long vowels, and diphthongs are represented by letters, while short vowels are represented by diacritics.

Angrezi (انگریزی)

Angrezi is a method of writing English using the Arabic script devised by Adnaan Mahmood. It is designed so that each sound of English is represented by one letter, and to be a standardised way for transcribing English in the Arabic script. Adnaan also thought that if the large population of English speaking Muslims want to write English in the Arabic script they could do so by using this version of the alphabet which includes vowels for easy reading and comprehension.

The name of the alphabet comes from the Urdu name for English, انگریزی (angrezi).


Yes.
Loglan is continuously being developed and modified, as the website shows. There are new reports about changes to the language (and proposals to do so). The CEO of the Loglan Institute, Randall Holmes, has written periodic reports on the language; the one from 2015 shows that several speakers have proposed changes, including the addition of new words (see Appendix 9). For the most part, excluding specific major developments like the Great Morphological Revolution of 1989, the structure has stayed the same, but grammar and vocabulary continue to grow and evolve.
In terms of the total number of speakers, we have little to no data. My impression is that since the split, Lojban has become more popular than Loglan. The Lojban community is largely Internet-based, and perhaps 20-200 people use it in some non-negligible capacity. Loglan's userbase is probably smaller than that, although I don't know how small. It's clearly non-zero, but not by much - perhaps 10 or 20 people.
Now, the question of whether Loglan is dead or alive rests in part on how you define a "dead language". I don't think anybody has ever learned Loglan or Lojban as a native language; you could therefore argue that it was never alive in the first place. So I suppose the best answer to your questions is that yes, Loglan is still being used and changed, but it's not "alive" in the sense of most languages.
The Loglan Institute considers Loglan to be alive because of the constant grammar/vocabulary changes; they define a dead language as one that isn't evolving. Based on that definition, Loglan is indeed alive.


Do any conlangs have verbs that change form depending on the object?

Yes.

I am not familiar with any “well-known” conlangs, but a quick search reveals that Klingon verbs inflect for both subject and object. This is a phenomenon called polypersonal agreement and it is very common in natural languages, and so it is only expected that it would also crop up in several conlangs. Among them, for example also my own, for which I just yesterday put up a puzzle that involves decoding the verbal system here.

I cannot currently think of any examples of a language which inflects for only the object, but it’s a rather low-hanging fruit and I cannot imagine that it has never been done before.


In what ways are well-known a priori conlangs inadvertently eurocentric?

While it's true that languages like Na'vi and Klingon (can't speak for Dothraki) do contain quite a few explicitly non-SAE (Standard Average European) features, it's worth noting that both Paul Frommer and Marc Okrand have stated that they were deliberately using less common and lesser-known features in their respective conlangs to make them sound more alien. Since avoiding features that would be considered common or familiar to their audiences (typically comprised of speakers of English and other SAE languages) was a goal during their language creation. I'd argue that deliberately avoiding all SAE features to make your language sound "strange" and "alien" is a sort of eurocentrism (though perhaps a less obvious sort than unthinkingly including all SAE features) in that your language ends up very influenced by European languages and their features.


How do I do interlinear glosses for a conlang?

Should we expect Leipzig Glossing Rules to work for all invented languages?

No, not all of them, but the set of languages for which they will not work is exceedingly restricted. Basically, just ask yourself "can my language be written in a primarily linear format?" If so, the Leipzig Glossing Rules are for you. If it is carried by sound, you can gloss it. That right there covers very nearly every language that has been asked about on this site so far. If it's a manual sign language, there's still an exceedingly good chance that you can gloss it. If it's a fully-2D non-linear writing system, the alterations you will have to make to the conventions to make it work then become sufficiently large that it would no longer make sense to call the result "Leipzig glossing". But those aren't exactly common.

How does one handle grammar that may not match up with the "standard abbreviations"? Lojban comes to mind, since they as a community reject that grammatical classes in Lojban have any counterpart in natural languages.

Exactly the same way the professionals do: by providing a glossary of your non-standard abbreviations.

Conlang audiences are just as likely to be an amateur audience, unlike the readers of linguistics academic journal. Is there a better way to gloss for a popular audience?

That depends on what you are trying to communicate to that popular audience. In some cases, a full gloss may not be needed, even for a professional audience. A simple set of parallel translations demonstrating the effect of a straightforward morphological or syntactic alternation, for example, may be sufficient for its purpose. But in the general case... I don't think so. Leipzig glosses are intended to be easy to understand, and they succeed at that about as well as it is possible to do in most cases.


How to say, 'Haters gonna Hate' in Toki Pona

The consensus answer (thanks Oliver Mason) for how to translate Haters gonna hate into Toki Pona is the following:
 tenpo ale la jan ike li ike

Tenpo ale la translates as at all times and captures the sense of inevitability in haters gonna hate in English. It also serves to rule out other possible readings such as the tautological bad people are bad. Here ike is used as "commit evil acts", one of which is presumably hating.

I interpret Haters gonna hate as a phrase for dismissing all criticism as inevitable or unfounded regardless of its content.
I don't think hate in this context literally refers to feeling hatred/enmity, but to hating on, which is not quite the same thing and covers things like insults and ridicule.
I think we strip out a lot of the detail of haters gonna hate and get something reasonable.
jan    ike    li   ike
person bad    PRED bad
bad    people are  bad

Since jan ike is so much broader than bad person in English, I think this does a good job of conveying the intent of the expression. People predisposed to ridicule or insult you are going to ridicule or insult you regardless of what you do.

The right way to combine the phrases you gave above would be
jan ike li awen pali e pilin ike tawa.

However, there are a few constructions in there I'm not sure about
li   awen  pali
PRED keep    do

I don't know whether you can use awen like this as an auxiliary verb of sorts to mark habitual or progressive aspect, as you seem to be doing here.
pilin   ike  tawa
feeling bad  towards

I don't know whether you can use an objectless preposition attributively like this. My guess is yes since prepositions besides e (if analyzed as a preposition) do not form a distinct word class in Toki Pona. I'm having trouble finding an explicit citation for the non-existence of prepositions as a distinct word class, this is the closest I can find.


How to model the change of script over time

The surface that things are written on. Runes were carved in trees and, as such, do not have curves. The Greek alphabet was written on tablets, and curved lines were possible. The Arabic alphabet was written quickly on papyrus. Also, some civilisations might prefer cursive script over others. Arabic letters differ whether they're isolated, at the beginning of a word, at the end or in the middle. So does your handwriting with the Roman script. But Arabic kept their cursive when the digital age came, and the Roman script got rid of it and created the same character.
Os (runes), psi (Greek alphabet, but modernised on a computer, see footnote 1), šīn (Arabic script, isolated)

ᚩ, Ψ, ش
Let's call the ancestor A. The two daughter languages will be called B1 and B2. A could be a pictographic script, from which B1 devised a syllabary but B2 kept pictographs. Or A was an abjad (alphabet without vowels) and B1 became an alphabet whereas B2 stayed an abjad.
Although language is passed on from mother language to daughter language with diachronics, script doesn't need to. In fact, you don't often see one script in the same language for three language-generations except in some cases like Latin (but Vulgar Latin wasn't really written much). Borrow a script from a neighbouring language. This is what I recommend doing.

Footnotes: 1) Ancient Greek part of the Rosetta stone. Greek characters in Unicode are in many fonts modernised, this is an example of typical Ancient Greek script.


How does one express "want to want" in toki pona?

mi wile ala e     ni:  mi wile e     ijo   nasa.
  I  want not <obj>-this I  want <obj>-thing crazy

The same principle as in "I do not want to drink water."

  mi wile ala e     ni:  mi moku  e     telo.
  I  want not <obj>-this I  drink <obj>-water


Is the Voynich manuscript written in a natural or constructed language?

We don’t know. It is written in an unknown script, by an unknown author. We don’t even know whether it is even in any language at all, or just random scribbles. Any attempts to connect it to a known language (such as Latin) have failed thus far.


Borrowing from conlangs into natural languages

The verb "to grok", having been coined by Robert Heinlein for his Novel Stranger in a Strange Land has gained significant popularity and is used with the same meaning as in the original language.

I am however not sure whether this meets the criteria of coming from a constructed language: To my knowledge the martians' language is clearly stated to be a full fledged language inside universe of the book, but "to grok" is one of the few (if not only) word to be given explicitly and there does not seem to be a full-fledged grammar or lexicon anywhere.

See also [1]; [2]


What tools are there to make this alien language?

Let's take modern Spanish Spanish and apply some nice natural sound changes to it, together with some plausible alterations to the spelling rules, and see what we get.
To begin with, let's take a Spanish text on which to apply the changes, so that in the end we have an example of Alien Spanish, with the goal of ascertaining that it is at the same time Spanish-like and alien enough. The chosen text consists of the first ten articles of the French Revolutionary Declaration of the Rights of Man and of the Citizen, as given by the Spanish Wikipedia:

Los hombres nacen y permanecen libres e iguales en derechos. Las distinciones sociales solo pueden fundarse en la utilidad común. La finalidad de toda asociación política es la conservación de los derechos naturales e imprescriptibles del hombre. Esos derechos son la libertad, la propiedad, la seguridad y la resistencia a la opresión. La fuente de toda soberanía reside esencialmente en la nación; ningún individuo, ni ninguna corporación pueden ser revestidos de autoridad alguna que no emane directamente de ella. La libertad consiste en poder hacer todo aquello que no cause perjuicio a los demás. El ejercicio de los derechos naturales de cada hombre, no tiene otros límites que los que garantizan a los demás miembros de la sociedad el disfrute de los mismos derechos. Estos límites solo pueden ser determinados por la ley. La ley solo puede prohibir las acciones que son perjudiciales a la sociedad. Lo que no está prohibido por la ley no puede ser impedido. Nadie puede verse obligado a aquello que la ley no ordena. La ley es expresión de la voluntad de la comunidad. Todos los ciudadanos tienen derecho a colaborar en su formación, sea personalmente, sea por medio de sus representantes. Debe ser igual para todos, sea para proteger o para castigar. Siendo todos los ciudadanos iguales ante ella, todos son igualmente elegibles para todos los honores, colocaciones y empleos, conforme a sus distintas capacidades, sin ninguna otra distinción que la creada por sus virtudes y conocimientos. Ningún hombre puede ser acusado, arrestado y mantenido en confinamiento, excepto en los casos determinados por la ley, y de acuerdo con las formas por esta prescritas. Todo aquel que promueva, solicite, ejecute o haga que sean ejecutadas órdenes arbitrarias, debe ser castigado, y todo ciudadano requerido o aprendido por virtud de la ley debe obedecer inmediatamente, y se hace culpable si ofrece resistencia. La ley no debe imponer otras penas que aquellas que son estrictas y evidentemente necesarias; y nadie puede ser castigado sino en virtud de una ley promulgada con anterioridad a la ofensa y legalmente aplicada. Todo hombre es considerado inocente hasta que ha sido declarado convicto. Si se estima que su arresto es indispensable, cualquier rigor mayor del indispensable para asegurar su persona ha de ser severamente reprimido por la ley. Ningún hombre debe ser molestado por razón de sus opiniones, ni aún por sus ideas religiosas, siempre que al manifestarlas no se causen trastornos del orden público establecido por la ley.

(Spelling change) Replace ce, ci with the, thi (as they are pronounced): nacen $\rightarrow$ nathen, sociales $\rightarrow$ sothiales etc.

(Spelling change) The acute accent indicates the position of the dynamic stress when it falls in a place other than where it's expected:

If the acute is on the last syllable before an n or an s, delete the acute and double the consonant: ningún $\rightarrow$ ningunn, demás $\rightarrow$ demass, razón $\rightarrow$ razonn. (It's not deleterious, since Spanish cannot have double consonants in that position.)

(Spelling change) Replace ñ with ny and ll with ly. (It could have been the chosen spelling, but wasn't.)

(Spelling change) Replace qu with k (or c, since by now we no longer have any possibilit of confusion); que $\rightarrow$ ce, aquellas $\rightarrow$ acelyas etc.

(Spelling change) Replace all is and us with y and w when they represent semivowels (also called glides, the less sonorous parts of diphthongs): igual $\rightarrow$ igwal, cualquier $\rightarrow$ cwalcyer.

(Spelling change) Delete initial and intervocalic h. (It is silent anyway.)

(Spelling change) Replace ge, gi with hhe, hhi, and then j with h:
ejecutadas $\rightarrow$ ehecutadas, ejercicio $\rightarrow$ eherthithyo etc.

At this point we have regular Spanish with a somewhat novel, but yet still consistent, spelling. Let's go and apply some natural sound changes:

Replace endings in -ad, -ades with -à, -ass. (Italian did it, for the singular; in the plural, Italian keeps -à unchanged.)

Delete final -o; in order to preserve the position of the dynamic stress, you must of course double the preceding consonant, as required by rule 2. (Romanian did it; we have lup for Spanish lobo, tot for Spanish todo etc.)

If the word ends in -wo, replace with -u.
If the word ends in -yo (at this stage of the modifications), replace the -o with -u.
If the final -o is the only vowel in the word, replace with -u.

Replace final -i with iy, final -e with i, and final -a with e. (Old French did the last one.)

Now do the plurals: replace final -os with -uy. (Romanian went even further, but let's keep it Spanish-y.) Replace final -es with iy. Replace final -as with ey.

(Slight, if any sound change.) Consistently replace vl and vr with br and bl, and elsewhere consistently replace b with v.

Finally, replace clusters of two occlusives (also known as stops) with the second one doubled, as Italian did.

At this point we have:

Luy ombriy nathen yiy permanethen libriy i igwaliy en derechuy. Ley distinthyoniy sothyaliy soll pweden fundarsi en le utilidà comunn. Le finalidà di tode asothyathyonn polítice iy le conservathyonn di luy derechuy naturaliy i imprescrittibliy del ombri. Esuy derechuy son le livertà, le propyedà, le seguridà yiy le resistenthye e le opresionn. Le fwenti di tode soveraníe residi esenthyalmenti en le nathionn; ningunn individu, niy ningune corporathyonn pweden ser revestiduy di awtoridà algune ci nu emani direttamenti di elye. Le livertà consisti en poder ather tod acelyu ci nu cawsi perhwithyu e luy demass. El eherthithyu di luy derechuy naturaliy di cade ombri, nu tyeni otruy límitiy ci luy ci garantizan e luy demass myembruy di le sothyedà el disfruti di luy mismuy derechuy. Estuy límitiy soll pweden ser determinaduy por le ley. Le ley soll pwedi proivir ley acthyoniy ci son perhudithyaliy e le sothyedà. Lu ci nu está proividd por le ley nu pwedi ser impedidd. Nadyi pwedi versi obligadd e acelyu ci le ley nu ordene. Le ley iy expresyonn di le voluntà di le comunidà. Toduy luy thyudadanuy tyenen derechu e colavorar en su formathionn, see personalmenti, see por medyu di sus representantiy. Devi ser igwal pare toduy, see pare proteger u pare castigar. Syend toduy luy thyudadanuy igwaliy anti elye, toduy son igwalmenti elegibliy pare toduy luy onoriy, colocathyoniy yiy empleuy, conformi e sus distintey capathidass, sin ningune otre distinthyonn ci le creade por sus virtuss yiy conothimyentuy. Ningunn ombri pwedi ser acusadd, arrestadd yiy mantenidd en confinamyent, exthett en luy casuy determinaduy por le ley, yiy di acwerd con ley formey por este prescritey. Todd acel ci promweve, solithiti, ehecuti u age ci sean ehecutadey órdeniy arvitraryey, devi ser castigadd, yiy todd thyudadann receridd u aprendidd por virtù di le ley devi ovedether inmedyatamenti, yiy si athi culpabli siy ofrethi resistenthye. Le ley nu devi imponer otrey peney ci acelyey ci son estrittey yiy evidentementi nethesaryey; yiy nadyi pwedi ser castigadd sinn en virtù di une ley promulgade con anteryoridà e le ofense yiy legalmenti aplicade. Todd ombri iy consideradd inothenti aste ci e sidd declaradd convitt. Siy si estime ci su arrest iy indispensabli, cwalcyer rigor mayor del indispensabli pare asegurar su persone e di ser severamenti reprimidd por le ley. Ningunn ombri devi ser molestadd por razonn di sus opinyoniy, niy awunn por sus ideey religyosey, syempri ci al manifestarley nu si cawsen trastornuy del orden públic establethidd por le ley.

Now, this is still sufficiently Spanish-y for a Romance speaker to be able to go through it, albeit slowly. It may or may not be sufficiently alien...
If still not sufficiently alien, continue sound changes:

Replace intervocalic r with rh and intervocalic s with r (Latin did the latter).

Replace s between vowels, or at the beginning of a word before a wovel, with w (Greek did it).

If still not alien enough, you may want to go through some chain shifts (as in Germanic for example).


ANADEW means "a natlang already did it even worse" or "a natlang already did it, except worse". In essence you thought of a strange feature for your conlang, but there is actually a natlang that has that (or a very similar) feature and did it worse than it is in your conlang.
If, for example, Pythagoras had made a click conlang (which somehow survived one or two millenia) with simple and easy clicks, then the "discovery" of the Khoisan languages with very complex click systems (worse for Europeans) would have made an ANADEW case.
I don't think that's the best possible example, you can find a few more at https://www.reddit.com/r/conlangs/comments/6yxo6k/anadew_game/ .


How do you model language changes with wave theory (areal developments)?

I have never tried to do it, but I think the approach you call "impractical" is the way to go. You need to maintain a grammar and a vocabulary for each town and for each period (say, a snapshot every 50 or 100 years) to keep consistency.

The good news that can save a lot of time is, that you probably don't need complete reference grammars for each step in the evolution: Start with a good grammar of the oldest stage of your language continuum and than write the grammars of the evolving dialects/languages in terms of differences to the old grammar.

Only when accumulated differences become too large to be handled well, write a full grammar again.


Strategies for dealing with limited/simple phonologies

One major problem is that a small phoneme inventory leads to longer words, as you have fewer short ones available. This kind of relates to the point you already mention, namely homophones: here you simply re-use a word form for multiple meanings.
Words would also sound more alike, even if different. This is one of the main problems I have with Hawai'ian (of course the vocab is mostly unrelated to the Western European languages I know), that words are hard to recognise for a learner, and then it's even harder if individual phonemes are different and completely change the meaning of the word.
This is fine for toki pona, which only has a small inventory of words anyway, but any more extensive language would quickly run into longer words or phrases.


Is a naturalistic language without countable nouns possible?

As a matter of fact, Mandarin Chinese can be considered to be such a language - it treats every noun as a mass noun. Every noun requires a "measure word" for counting, like "bottle" in "four bottles of water" or "sheet" in "ten sheets of paper". Chinese has a considerable list of these (https://en.wikipedia.org/wiki/List_of_Chinese_classifiers) but there's no particular reason that a language with only mass nouns would need to have so many classifiers.


Can Pokemon language encode enough information to be a language?

From what I remember from the cartoon, Pikachu could only say certain permutations of its name, with any combination of vowels elongated.

3 syllables   pikat͡ʃu   8 words
2 syllables   pika      4 words
1 syllables   pi        2 words

Pikachu is also capable of producing at least 4 different tones:

Tone     IPA   Made when
High     ˥     Excited
Mid      ˧
Rising   ˧˥    Curious
Falling  ˧˩    Disappointed

So, knowing this, Ash's pikachu should be able to say at least 584 distinct "words", which is well above the toki pona threshold.

Sadly it's pretty much impossible for this system to match the lexicon size of a natural language. Using an 8 tone system and adding primary and secondary stress brings the number of distinct words up to 25104, which is significantly larger than the Esperanto lexicon but still far away from that of a natural language, which is around 200K words.

From here on you could introduce some questionable features like 8 more tones, 7 different vocal registers, or the ability to say different permutations of its name (which is probably not as dodgy but also imagining pikachu say /ka.chu.pi/ makes me extremely uncomfortable).
The best way in my opinion would be to introduce the syllabic thunder shock ⚡, which would require pikachu to release up to three thunder shocks whilst saying a word, all for the good cause of bringing the lexicon size of Pika-ese to a final 198688 words.

(No wonder Meowth learnt how to speak a human language, imagine being stuck with a one-syllable name.)


What are resources for conlangers designing a knot writing?

I made one such conscript. I found another for writing English.
Some useful resources include:
Ashley's Book of Knots
Animated Knots
Various macrame websites and the concept 'sinnet' (you could decorate "nodes" within)
I think khipus and knot-writing most fascinating and I have greatly enjoyed the exercise. If people comment with specific curiosities, I will try to help. This question doesn't, per se, require an "answer" but I hope posting it may be useful and fruitful for the community.
Thanks, jk - Reinstate Monica, Andrew Ray, and curiousdannii for your input about correct posting!


Does Esperanto have any words that mean more than one thing?

One also has to bear in mind polysemy: a word that might correspond to one concept in English might translate to two different words in Spanish or German. A classic example is “corner”, which can be translated to Spanish as either rincón or esquina, depending on whether one is talking about an “inside” or “outside” corner. I went to check how Esperanto deals with that particular word and found that eo angulo refers not only to both kinds of corners, but additionally also means “angle”.

So yes, Esperanto clearly has polysemies.


Are there any sites you can use to develop an online course for your own conlang?

Apparently folks can do this with Memrise, as evidenced by the Sajem Tan lessons.

There's been talk that I found on Duolingo forums, but if they're at all serious, they probably won't allow "dabbling". You'd need a serious effort to make and maintain enough lessons for people to actually learn a language.


What is the difference between tense and aspect?

When discussing tense, aspect, and mood, it's important to distinguish a given language's grammatical markers from the abstract concepts being described. Thus, linguists use the words temporal reference and aspectual reference to describe the abstract ideas being described, while the words tense and aspect are reserved for when such reference is marked grammatically.

The simplified explanation for tense and aspect usually given is that tense describes when an event occurs and aspect describes the internal temporal structure of an event. However, this doesn't give a ton of easy answers to "is this grammatical form marking tense, aspect, or both?" Formal semanticists actually have a relatively simple framework for how temporal reference and aspectual reference are defined, the basic concepts of which can be helpful when designing your conlang's own tense/aspect system.

The Neo-Reichenbachian Model

Imagine a timeline:

Earlier                                  Later
<-------------------------------------------->

Now, imagine there are two spans on that timeline (the fact that they're spans is important -- nothing is truly instantaneous). The time when you make an utterance is called the utterance time (or UT), and the time that you're talking about is called the topic time (or TT).

Temporal reference describes the relationship between the TT and UT. Past temporal reference is when the TT precedes the UT; future temporal reference when the TT follows the UT; and present temporal reference when they overlap.

Past:
    <-------------------------------------------->
                |--TT--|          |--UT--|

Future:
    <-------------------------------------------->
          |--UT--|                  |--TT--|

Present:
                            |--UT--|
    <-------------------------------------------->
                     |-------TT-------|

This seems pretty intuitive -- if the section of the timeline you're talking about precedes the time you make the utterance, you'll use the past tense; if it follows it, you'll use the future; and if they overlap, you'll use the present. Simple, right?

But what of aspect? Well, aspectual reference isn't as transparent at that. To describe aspectual reference, we'll need to pick out a third span that timeline -- the time when the event being described actually happened. We'll call this the eventuality time (or ET).

"But wait!" you might object. "Isn't that the same as the topic time? If I'm describing something that happened, surely the time I was talking about is the same as the time that it happened." However, there is a difference, and it's exactly this difference that gives rise to aspectual reference. Consider the English past perfect in a sentence like the following:

  Yesterday he had gone to the store.

The English past tense includes past temporal reference, and we've established that this means that the topic time is before the utterance time -- something which is explicitly confirmed by the temporal adverb "yesterday" giving us a more specific topic time. But when does the him-going-to-the-store happen? Probably not yesterday, right? Well, this is because perfect† aspectual reference is when the eventuality time precedes the topic time -- aspectual reference describes the relationship between the eventuality time and the topic time. It for this reason that the past perfect is used by English speakers for the past-in-past.

Past Perfect:
    <-------------------------------------------->
          |--ET--|    |--TT--|     |--UT--|

But you can also have the present perfect, right? Well, let's combine our descriptions of the present tense and the perfect aspect and see what we come up with.

Present Perfect:
                            |--UT--|
    <-------------------------------------------->
        |--ET--|     |-------TT-------|

Here, the topic time and utterance time overlap, which is why you can't say something like "Yesterday he has gone to the store." However, the eventuality time precedes the topic time, so you're describing an event that happened in the past in relation to the present. And indeed, this is how we see the present perfect used in English.

This is far from the most interesting thing aspectual reference can do, however. Let's discuss the popular aspectual references, perfective and imperfect. For those who don't know, perfective and perfect are two different things. Perfective is often described as simply viewing an event as a point on a timeline, and imperfect as viewing it as a span. How do we define this as a relationship between eventuality time and topic time?

Well, a simple way people do it (ignoring a few other related thorny semantic problems that few here will care about) is by defining the perfective as when the eventuality time is contained within the topic time and the imperfect as when the topic time is contained within the eventuality time.

Past Perfective:
               |--ET--|
    <-------------------------------------------->
        |-------TT-------|        |--UT--|

Past Imperfect:
               |--TT--|
    <-------------------------------------------->
        |-------ET-------|        |--UT--|

This results, at least formally, in the same sort of perspective shift we try to intuitively describe as changing the event from a "point" to a "span".

Note that tense and aspect vary between languages a lot, and even related languages can't be counted upon to have the same semantics here. After all, the French passé composé, while very similar in form to the English present perfect, does not share the same semantics (it's more of a perfective). Additionally, while a given language's system of tense and aspect will often combine a tense and an aspect in a certain inflection (such as the perfective past tenses in many European languages), this doesn't mean the two are wed cross-linguistically.

In fact, I hope this answer has given some conlangers the tools to try and invent their own tenses, aspects, or combinations of the two that they haven't themselves encountered cross-linguistically. Be creative!

In short:

Temporal reference is the relationship between the utterance time (when you say something) and the topic time (the time relevant to the discussion at hand).
Aspectual reference is the relationship between the topic time (see above) and the eventuality time (the time when the event being described actually occured).
Tense is the grammaticalization of temporal reference.
Aspect is the grammaticalization of aspectual reference.
Things called "tenses" in natural languages (as well as in conlangs, to be honest) are often conflations of tense and aspect (and sometimes even mood, but we're not here to talk about that).

†When I refer to perfect aspectual reference, I'm actually more specifically describing what is known in semantics as the existential perfect. Perfect forms in English and many other languages include other types of perfect aspectual reference (universal, resultive, etc.) that differ subtly in their semantics, and other aspectual and temporal baggage as well; this is, however, probably not particularly interesting or relevant to most people here at this moment.


Can Kēlen truly be considered verb-free?

Using the Natural Semantic Metalanguage as a good baseline of what a human language can communicate, there are several core verbs:

Mental predicates: THINK, KNOW, WANT, FEEL, SEE, HEAR
Speech: SAY
Actions, events, movement: DO, HAPPEN, MOVE
Location, existence, specification: BE (SOMEWHERE), THERE IS, BE (SOMEONE/SOMETHING)

LA is clearly polysemous for THERE IS, BE (SOMEWHERE), BE (SOMEONE/SOMETHING), and probably also marks PART in reverse.

NI probably covers DO and MOVE.

SE is even higher level, expressing the verb of give, as well as primes like FEEL and SAY.

So the claim that Kēlen does not have verbs is patently false.

There are in fact natural languages with even more restricted verb inventories than Kēlen, such as Jingulu, which has been analysed as only have verbs for go, come, and do. (I haven't seen an NSM style analysis of Jingulu, I wonder how they would see the verbs like THINK etc being expressed in Jingulu?)


Were Tolkien's Elvish languages based on known natural languages?

Tolkien started really early in his life to develop languages. Started at 13 and developed languages till his death.

  Tolkien was a professional philologist and a specialist in the Old
  English language. He was also interested in many languages outside his
  field and developed a particular love for the Finnish language (he
  described the finding of a Finnish grammar book as "entering a
  complete wine-cellar filled with bottles of an amazing wine of a kind
  and flavour never tasted before".

  Finnish morphology (particularly its rich system of inflection) in
  part gave rise to Quenya. Another of Tolkien's favorites was Welsh —
  and features of Welsh phonology found their way to Sindarin. Numerous
  words were borrowed from existing languages, but less and less
  obviously as Tolkien progressed. Words that are an exact match with
  existing Welsh words can be found in the early drafts of Tolkien’s
  manuscripts published as The History of Middle-earth,[4] but attempts
  to match a source to a particular Elvish word or name in works
  published during his lifetime are often very dubious.

Source: Languages (Tolkien Gateway)