What symbols should I use for phonemes when I have many vowels?

One possibility is to use German-style umlauts, i.e., ü for /y/, ö for /ø/, and ä for /æ/; you can keep the symbol œ for /œ/. I'd recommend against having both ae and œ in the writing system because of confusability. The choice of tilde for nasalisation is a good one, IMO. The most problematic case are the two different kinds of a-sounds, but there are some African languages just going with a and ɑ (and there is also an uppercase letter for the ɑ in Unicode, it is named Latin Alpha). All the symbols are readily available in Unicode and should not pose insurmountable difficulties in text processing.


How to naturally evolve verbs into adverbs or dependent clauses?

This is more a lengthy comment on your question than a real answer, but comment space is restricted ...

You are undertaking a very difficult task by setting a starting point and an end point and asking for natural development between the two. This is difficult even when it is known that such a natural development exists because the two languages are attested natural languages and not constructed.

We know sound laws really well, and also the process of grammaticalization is fairly well understood. The evolution of different basic word orders is still under research, we know that it has happened but how exactly it happened, is less clear.

It seems that your are needing some grammaticalisation to get from the verb pfufi to the adverb pfufe. Here's a suggestion: Add a particle ye meaning roughly "like" to your proto-language, and the phrase pfufi ye will fill the role of an adverb. It is easy to conceive, that pfufi ye evolves to pfufe by just dropping one syllable (syncope). To make tushu from tushi a particle like vu might be applicable, but I have some difficulties to define its original meaning.

I think that language change is easier to "grow" than to "plot", i.e., it is easier to just apply changes to a proto-language and watch where they lead to than to interpolate between two stages of a language.

Of course you can invoke language contact to achieve a particular change in your language evolution, as kind of last resort to save the plot. Just don't overuse this.


Is any of the Wakandan writing in Black Panther used for something other than English?

It's important to note that there were two Wakandan scripts used in the set design of Black Panther -- one is the transliteration alphabet seen here, while the other is a se of symbols based on Nsibidi that is more logographic in nature. They were used on different parts of the set, with the more logographic script occurring in a lot of the more traditional contexts and the alphabet occurring more widely throughout the set.

The Omniglot page for the script includes text written in both English and Xhosa using the script, but the Xhosa text seems transliterated from the romanized orthography for Xhosa. That said, since the author described the alphabetic script as a "more evolved" version of the logography, it's possible that it was deliberately designed to be similar to the Latin transliteration of Xhosa? Granted, that doesn't seem particularly in-character for the Wakanda depicted in the film, but who knows. Perhaps we'll learn more about the script in the inevitable sequel.

I think we can say that the alphabetic script is not only used to transliterate English as it is in the title cards. Consider this image from the article, which features portions of some Wakandan signs:

The glyphs on the rightward sign are difficult to make out and may be part of the logographic script, but those on the leftward sign read "DJO" in the Wakandan script -- as neither DJO nor OJD are allowable clusters in English, it seems unlikely that this is a portion of an English word transliterated into the alphabet.

However, it definitely is used to transliterate English even outside of the title cards. Let's look at the text on the throne in this poster:

The text on the lefthand side of his throne clearly reads "WISDOM" and the righthand text reads "LOYALTY" -- obviously an English transliteration. This is particularly egregious given that this is the king's throne, which arguably shouldn't feature the modern Wakandan script at all, much less Wakandan being used for English. However, it is admittedly a poster, so it's not really properly in the movie -- I cannot find a screenshot of the base of the throne from the actual film, so I can't say whether the text is the same there.

The alphabetic script is frequently used in the set design of the lab, but the only screenshots I can find of it are either too blurry to make out or just feature simply the glyphs overlapping each other for aesthetic in a screensaver-esque fashion.


How does one determine the date a constructed language was invented?

For auxiliary languages it's usually publication date of the first grammar/dictionary released to the public or the first work dedicated to the language, whichever comes first.

For Esperanto this was Unua Libro, which was published in 1887 - more than a year after Zamenhof began working on the language. Wikipedia also lists the year of creation of Occidental as 1922, the year de Wahl published the first edition of the Kosmoglotta magazine, despite there being evidence that the language was used much before then, both in private conversation (letters etc.) and even a publication written entirely in Occidental.

The "date of creation" for other types of conlangs seems to be less well-defined, although I'd expect that fictional languages would be associated with the publication of the first book/movie/game that uses them (perhaps with the exception of Tolkien's languages). Wikipedia also uses the day Lojban began being developed as its creation date.


Is mathematics considered a constructed language?

I think Programming and Mathematics fail to meet the standard because, despite being more precise, they are ultimately nowhere near as expressive as a language like English.

Per request I will expand on my answer. Take, for example, the English sentence "Jane missed the bus this morning and couldn't get to the office in time her interview, needless to say, she was not selected for the position." There is no way to express that in any programming language that I know of.

var Jane = {Name:"Jane", Employment:"Unemployed", Bus:data.Buses[4]};
data.Buses[4].Depart("2019-10-05 07:30:00");
Jane.ArriveAt(data.Buses[4], "2019-10-05 07:45:00");

I won't go on trying the futile exercise of typing out a description of events in Javascript. Note that without knowing English the code makes no sense. Anything in code that isn't a keyword like "if" or "foreach" or "function" isn't part of the language and so you can only describe procedures for moving bits around, one way to illustrate this is to convert my Javascript to do the same thing, but with different variable names - the program will be exactly the same as far as the language specification goes and the resulting executable.

var x = {a:"", b:"Unemployed", c:y.z[4]};
y.z[4].dp("2019-10-05 07:30:00");
x.w(y.z[4], "2019-10-05 07:30:00");

If those two paragraphs mean the exact same thing as far as the language is concerned, you've completely failed to communicate anything useful. Computer scientists working on artificial intelligence are working to make systems where "bus" is a keyword, there is an idea of "bus" in the language. Until that technology is fully realized, we will be stuck with programming languages that are limited to describing things a computer can understand, a much lesser standard than what a human can. This is what I mean by less expressive.


The particle la in Toki Pona is used mainly for two scenarios.
The first scenario is for the If/when something, then that condition. The la particle is placed in the second half of a sentence. Some examples:

mi lape lili, la mi pilin ike (If I sleep a little, then I feel bad
or When I sleep a little, I feel bad)
sina moku e telo mute, la sina anpa e telo mute lon tenpo lili (If
you drink much water/liquid, you are going to pee much in a short time)

The second scenario is for the context, like time, possibilities, or even non yes/no questions. The la particle is placed in the first half of a sentence. Some examples:

tenpo pimeja ni la, mi lukin e lipu sin (I am going to read the new book tonight)
tenpo suno pini lili la, mi kute mute e kalama musi (Yesterday I listened to much music)
ken la, pilin pi meli lili li pilin ike (Maybe the girl's sad —literally, "Maybe the heart of the girl feels bad")
tan seme la, kulupu pi jan lili sona li tawa ala tomo sona? (Why are the scholars not going to the school?)

Hope this helps!


Is it possible to make a declension system that DOESN'T limit what nouns can end in?

Ignoring the lost natlang, I'll just answer the title question:

There are several possibilities to let nouns end in any phoneme of the language and still have case inflections:

Most simple: Have a zero ending in the nominative singular
Base your inflection on prefixes (like in Bantu languages) or infixes (like in Semitic languages)

BTW, inflections with thematic vowels (like in Latin and Greek) aren't particularly difficult to remember, because the thematic vowel is easily recognisable throughout the whole inflection paradigm.

PS Many natural languages have only a restricted set of allowed phonemes at the end of a word. Classical Greek is an extreme example of this kind of restriction, but also German has Auslautverhärtung aka final devoicing: Final consonants are always devoiced. This feature does not show up in writing but only in the spoken language.


If 'Amlonde' were a word in Sindarin or Quenya, what would it mean?

There is actually a neat analysis in Quenya according to a Tolkien Dictionary Site:

am-: is a prefix that means "up"
londë: means "(landlocked) haven"

So you can imagine it describing a place that once was a harbour, but through geographical changes has become landlocked, and is possibly on a hill or mountain. Or it could be a refuge, a safe place in the mountains.


Are there any rules of thumb for number of "steps" between two points in a language's natural development?

It’s relatively hard to say. First, some general numbers:

Over 1000 years, Old High German split into the various southern German dialects, including Swiss German and Standard German. While differences are very noticable, many developments were parallel and speakers usually don’t take long to get accustomed to the differences. A similar time depth can be claimed for English vs Scots. Old High German itself is not readily intelligible to the modern speaker, but many words are recognizable.

2000 years ago, we had Latin and Proto-Germanic, the ancestors of the Romance and Germanic branches of Indo-European. While the modern languages all show clear similarities in most regards of the language, they are as a general rule not mutually intelligible and speakers need to invest a lot of time to learn another of those languages - but still much less than with an unrelated language. Proto-Germanic and Latin are both quite different than the modern languages, showing vast differences in morphology and syntax, as well as having undergone many sound changes since. Nevertheless, with some knowledge on etymology, words can readily be recognized for what they are in a written text.

About 4000-6000 years ago, we have PIE. At this point, the language is no longer immediately recognizable as being related to a modern European language. The grammar is very different - just as an example, PIE verbs inflect for three persons and three numbers, but not directly for tense or aspect, which are instead marked with various more-or-less productive derivational affixes. The phonology would also look very out of place in modern day Europe. And for most roots, even if they didn’t change much phonologically, there was probably a semantic shift somewhere between PIE and English. The average English speaker will understand exactly zero words in a passage in Serbian or Punjabi.

But there’s another side to this as well. General tendencies are fine, but what about individual languages? If you compare Italian and French to Latin, then it’s plainly obvious that French has changed more, at least with regards to phonology and morphology. Similarly, comparing English to Icelandic, the latter is clearly more conservative (though no where near as much as some people might make you believe). To me, French and English look like they are 500+ years further in the future than their contemporary siblings — in reality of course they just underwent some more drastical sound changes that in turn messed with their morphology, which in turn forced changes to the syntax. People try to ascribe those changes to various factors, usually external ones such as a large number of foreign learners, but most of this is not grounded in actual science and just speculation.

As such, no definitive answer can be given. I find the time depths I gave above to be good rules of thumb, but single languages may deviate from those quite a bit. To achieve such results, it’s important to apply changes not only to the phonology, but to all parts of the language — especially the lexicon.


Are there concrete examples of slang developing within a conlang?

Wiktionary has a list of Esperanto internet slang but most of these I've never seen or heard used before (at least in the main esperanto chats on Telegram).

Esperanto slang terms I've heard or used

krokodili - to speak in a language other than esperanto in a group of esperantists. No one really knows where it originated but the most popular story seems to be that it's because crocodiles have big mouths and small brains. "Ne krokodilu" is a very commonly used phrase.
sal - hi (short for saluton)
kvf - how are you (abbreviation of kiel vi fartas)
mdr - lol (multe da ridoj)
mns - idk (mi ne scias)

Interjections

ho ve (occasionally just "ve") - oh geez
(according to this post on Esperanto SE the literal translation is "oh woe" but who says that)
8, ok, okej - k, ok, okay
("ok" is the word for eight in Esperanto, mdr.)
ho - oh
jes ja - yes, indeed
(according to this post on Esperanto SE "ja" can be used in other situations, but I have never heard or seen it used other than after "jes")
Fek' - f*ck
Kio la fek - what the f*ck
(This is an obvious anglicism and considered "grammatically incorrect" by many esperantists, who will tell you it's actually kio feke)
Volap*ko - "the v word". More offensive than all the offensive words you know combined.


How can I become a professional conlang designer?

The list of ways to make money with a conlang is short, so step one is to be creative.

Write Genre Fiction Books.
Authors do make a living writing and selling books, sometimes with an artificial language bundled with it. Wardesan, Láadan, Tolkien's books are good examples. I'm guessing the conlang part though is reducing their income, they could write more books if they skipped writing a conlang. Personally, I'd buy a book with a conlang if the author tried to make it simple enough to enjoy for 10 to 20 hours. Instead we get unusable languages that require 2000 hours of study to appreciate them, same or worse than a natural language. And I'm an outlier, so I'd imagine regular genre fiction buyers see a bundled language as a low value gimmick.

Communication Systems for the Disabled.
Blissymbols made money, albeit in a rather dishonorable way by suing the institution that was trying to help the profoundly disabled communicate with a symbol board, which was in essence an artificial language. I spoke with a specialist in the more modern versions of these, and often vendors don't even bother to acknowledge that symbol boards are not English, but conlang-like systems with all the challenges.

In the realm of conscripts, there is a commercial writing system for ASL. I'm failing to re-find the link.

Historical BSL was essentially a franchise and BSL was something of a trade secret.

Movies.
Movies have been hiring professional linguists (Klingon, Na'vi) The Klingon dictionary and Avatar handbook sold a lot of copies, but the authors both became professional linguists first, and these books are really side projects.

Selling learning materials.
This has got to be the worst way to monetize a conlang. The artificial language section of any large library has to be littered with books of people who thought they could sell a lot of copies of their grammar summaries, workbooks and dictionaries. No one wants the grammar summary. What they want is to meet their significant other by learning a language which brings me to...

Esperanto
Esperanto actually has economic activity, but the language is already written. Building a language starts with grammar and vocabulary, but to extract money from people, people need to learn it. If your interest in conlang building is in the community building part, then it might make more sense to make a living working with an existing conlang that has attracted a community, complete with conferences, etc. That said, I'm guessing no one is getting rich off of Esperanto, but there are teachers of Esperanto, etc.

Games
There have been reports of people writing full languages for computer games, card games. Magic the Gathering's Phyrexian comes to mind. So far, these have been gimmicks and the amount of money, I'm guessing is not a lot. Some of the game makers don't even bother to publish the grammar and dictionary! This makes it sort of into a laborious game of decipherment.


Yours is a very interesting and legitimate question, but in the light of what we know from the languages of the world, what you ask is might not be what you mean to ask. Let me expand a bit below.

To answer your question in brief: no, your language does not need a Dative, but yes, your language needs a device (or "construction" in Construction Grammar terms) to express the third argument (also called the "indirect object") of verbs that take on three arguments (subject, object, indirect object).

Now, whether you have separate devices (constructions, or in your case "cases", no pun intended) for semantically different indirect objects or not, that is up to you. Since you already have a Benefactive case that could express an indirect object (whether that is semantically a recipient or a beneficiary or else), then you can use that to express an indirect object that is a simple recipient. So, note that there can be a mismatch between syntactic arguments and semantic arguments (for example indirect object vs. recipient, benefactor, etc). Moreover, depending on what linguistic framework you assume, things can be slightly different. Here I am adhering to some form of (Radical) Construction Grammar.

For example, since you have a Benefactive case and a Lative case you could use the former in sentences like "I gave the book to the man" and "I opened the door for the woman" and the Lative case for "I went to the market" and "I am throwing a stone at you". But again, that is really up to you, as also hinted at in other answers/comments.

The drafts of the first two chapters of Croft's Morphosyntax: constructions of the world's languages expand on this. See https://www.unm.edu/~wcroft/WACpubs.html.


Has AI technology yet provide a language composed of multiple human languages yet?

Not really AI, but the vocabulary of the two logical languages Loglan and Lojban was created algorithmically from the vocabulary of pre-defined source languages. In this case, the phonemes of the words were picked by the algorithm which is different from the formation of a creole where whole words are picked by the human speakers.


Unfortunately, the English Wikipedia does not have an article on Slavic toponymy yet, the best attempt I am able to find is Bulgarian placename etymology giving at least some hints. You can find interesting Slavic roots to play with in the article on Slavic given names.

Additionally, there are some Slavic based conlangs out there, you can honour one of them by employing it in your fictional world, to drop just names Slovio, Interslavic, see also Pan-Slavic language for an overview.


State-based analogue to distributive case

Interesting concept for a case. In my interpretation this kind of an abstract distributive case would apply in sentences like this one (a probably very clumsy reformulation of a famous first sentence in literature)

Every unhappy family is different in their unhappiness.

I looked up the really case-rich conlang Ithkuil and did not find a precedent for this kind of case. Feel free to name it by any name you like. When you don't have an own idea, I suggest respective case for that one.


What to do when my conlang has a word that means something in one of my languages?

These sorts of coincidences are somewhat inevitable. Just try to accept that there's a limited number of ways to arrange sounds in your language, and some will sound similar to words in other languages.

When I was trying to learn Hungarian, I came across a number of words that reminded me of words I knew in English and other languages. Some examples:

 repülőter "airport" /  re-polluter
 csillag"star" /  ceiling
 és "and" /  es "it is"
 a nap "the sun" /  a nap
 a bolt "the store" /  a bolt
 öt "five" /  otto "eight"

I also had a recent case on the CBB where I posted my conlang Atili's word for "citrus" zilu, and immediately got asked if I borrowed that word from Kankonian (another conlang) tzelua "citrus." I hadn't. CBB thread

Then there is the fairly well-known case of the Mandarin filler phrase 那個 / 那个 nèige, which sounds to many English speakers like a racial slur. See this posting on the Chinese language stack for more details: Very frequently used word in Mandarin that sounds like "nica" or "nigah"


How can I add irregularities to a morphological paradigm?

One possibility: perhaps your "-a- for plural" derives from an ancient word for "many" that was of a different declension, having different endings, so you could posit:

S  -o / -og / -ot / -om / -ol
vs
P  -a / -az / -asis / -amis / -ay

Another possibility: the historical importation of a foreign declension pattern into words of certain classes, which practice later infects native words of other classes either in whole or in part.

Consider the Latin words that have Greek declension and extrapolate from there.

A third possibility: the later "regularisation" of ancient defective words actually introduces an irregularity. For example, your modern word for "mob" might be an ancient plural form of "person", so you could posit:

S -a / -ag / -at / -am / -al
vs
P -a / -az / -asis / -amis / -ay


What does xorlo do, and is it an official part of the Lojban language?

xorlo is an official part of the Lojban Language. The Complete Lojban Language does not contain information about xorlo, and is no longer guaranteed to be entirely accurate. The Committee for Developing Lojban (BPFK) voted 11-0 to include xorlo in the official record as a part of the Lojban language. The proposal is not finalized until the BPFK declares their work finished, but it is extremely unlikely to change, as it has become an integral part of how the language works conversationally.

In essence, xorlo changes the meaning of two particle articles in lojban: lo, and le.

lo as an article used to indicate that you were talking about a set of objects which are truthfully what you claim they are. Nothing about them indicates that they would be anything else. For example, "lo jgena" meant "some things that are, to our best perceptions, knots."

Now, it doesn't say anything about perceptions, or the truthiness of what it is. It just means "any or some." It becomes the most generic article you can use in lojban, in place of anything else, because it is vague. "lo jgena" now means "any/some knot(s)," without qualification or ulterior statement about veracity.

le as an article used to mean "some things I have in mind, which I am describing." For example, "le jgena" meant that you had some knots in your head. The change to le is very minor in this context, and its pure meaning hasn't actually changed. The only difference is that it now exists only to be used when you have specific images of something in mind. Now, if I tell you "le jgena," you know I mean something more specific.


Is there a specific term for a constructed writing system purportedly used for a conlang but actually for a natlang?

I don't think there's already a word for this exact subset of scripts.

However, I think such a term would be a useful one -- we certainly have to refer to these sorts of scripts in the conlanging community -- and I think there are a number of options here.

1. Circumlocution

We could refer to these sorts of scripts in paraphrastic ways, like how you have in your question. "Transliteration alphabet" and "substitution cipher" both work for this purpose. However, I don't think this is a particularly attractive option, as these are long and rather unwieldy. Shortenings of these phrases end up being pretty ambiguous, as well. "Transliteration" in particular is usually used to describe completely separate things entirely, so using it in isolation to refer to these scripts would be confusing at best, and "substitution" is too vague.

2. Neologism

Since these sorts of scripts are really the neographic equivalent of relexes, we could also coin a new term like "relex" to refer to these scripts. Just spitballing, here are a few examples of the sorts of coinages that could work:

transbet (from "transliteration alphabet")
subscript (from "substitution script" -- though this word does obviously already have another meaning so that might not be desirable)
rescript (from analogy with "relex")
keychain script (because these sorts of scripts are easily used to sell keychains with people's names on them 'in another language')

There are any number of ways that such a term could be derived beyond these, but I feel that in order to have a term that describes this subset of scripts, some sort of new coinage is necessary.


Adding entire musical concepts to expand vocabulary

There is a precedent for the use of a musical tone scale in constructed languages: Solresol, a philosophical language constructed in the 19th century. Some natural languages also have a whistled mode, most notably El Silbo and Pirahã.

I am not aware of a language—neither natural nor constructed—that incorporates the concept of rhythm or other musical concepts.


Examples of the combination of 2 independent symbolic scripts

The obvious comparison to make here is to Japanese, as it's a real-life hybrid script and is currently the only non-Chinese language to use them. However, it's important to consider that Japanese did not have an existing writing system when Chinese characters were brought over, and for quite a while the Japanese elites wrote strictly in Classical/Literary Chinese, even after the evolution of hiragana (which were more often used by women).

Given that you have actual Chinese people in this exiled empire you describe, they will almost certainly be writing in Literary Chinese but speaking some form of vernacular (the specifics of which will depend upon where in China they've come from), so it's possible that Chinese characters will be repurposed to write Nahuatl, particularly if the Chinese become the dominant group in the area. Or it's possible that the opposite will happen, particularly if the Aztecs are the dominant group, and the Chinese will begin to write their language (be it Literary Chinese or their spoken vernacular) using the Aztec script.

The idea of the Chinese script influencing the Aztec script but the opposite not being likely seems to be based on some misplaced ideas about simpler characters being inherently better and more likely to catch on -- which script becomes dominant is more likely to be influenced by the sociopolitics of this situation rather than any inherent qualities of the script. Also be sure to keep in mind that different scripts are better for different writing materials -- will the Chinese be able to continue to produce the kinds of paper, ink, and brushes they're used to in the Americas? These are the sorts of things you need to research, ponder, and decide for yourself.


There is one big point here that really ties it all together:

Languages have history

Any conlang that wishes to look naturalistic therefore needs to emulate history as well. I’ll show in what ways history can manifest with a bunch of examples from different areas.

Orthography

Almost no language with a history of writing has a fully regular orthography. Even if there are regular writing reforms, some aspects of the orthography will just be considered “part of it” and stick. English is of course a very extreme example of this, but you don’t need to take it that far. German for example generally has a rather regular orthography. But the digraph ⟨ie⟩ represents a long /iː/, reflecting that in the past (and in some dialects until the present) there was a diphthong /iə/ in German, which became to be pronounced that way. It also has two separate graphemes for the phonemes /ɛ eː/, namely ⟨e ä⟩, reflecting whether the sound originates from a fronted /a aː/ or not. On top of this, there are some segments which have unpredictable pronunciation: word final -ig for example is pronounced /ɪç/ instead of expected /ɪk/. In short, unless your writing system was designed very recently by linguists, it likely shows leftovers from the past. In the most extreme cases, writing systems can lag behind centuries (English, French, Tibetan), but even if they don’t they can preserve some old features.

Morphology

Most languages with inflections show some degree of irregularity among them. This can manifest in many degrees, from almost entirely regular (Swahili has only one class of six slightly irregular verbs, one of which is suppletive in the present tense) to a basically complete lack of predictability (Navajo verb stems have defied any attempts to find rules for their inflections thus far. There don’t seem to be distinct paradigms, every verb does its own thing!). However, these irregularities are not random. To show what I mean, compare these two sets of declensions. The first two are latin singular nouns (in an less traditional order), the second two made up on the spot.

NOM filius rēx      kwero   tulya
VOC filiī  rēx      kwerap  tulte
ACC filium rēgem    kweruf  tultsu
GEN filiī  rēgis    kwerim  tulne
DAT filiō  rēgī     kwerx   tulum
ABL filiō  rēge     kwert   tulwo

Two things should stick out:

The Latin forms of rēx show two distinct stems, those ending in /k/ (rēx, where the spelling hides the fact that really it’s rēc-s) and those ending in /g/ (all other forms). Looking a bit closer, we can see that the /g/ appears exactly before those forms with a vowel in the suffix. Intervocalic voicing (which accounts for /k/ becoming /g/) is a common sound change and applies here.
While in both languages, some of the affixes seem to be unrelated, there are still patterns: nominative takes -s, accusative takes -m, genitive has an -i in the suffix… If we added other paradigms into the comparison, even more such patterns would arise, indicating that they really originate from a much more regular system that got changed up over time by various factors like sound changes. In the made up language, on the other hand, the affixes are entirely random, and this causes the irregularity to look more unnatural than if everything took the same affixes.

Phonology

Consider the Japanese consonant inventory. It looks something like this (omitting allophones):

  m |   n |   ɴ |
p b | t d | k g |
    | s z |     | h
    |   r |     |
    |   j |   w |

What this table does not show however is that /p/ is significantly rarer than /t k/. Why would that be? Simply because many instances of that sound somewhat recently shifted to what is /h/ in modern Japanese. In other words, a sound change caused a significant imbalance in the distribution of sounds. If one were to simply generate words with a word generator, not paying attention to the history of the language, all sounds would show up with similar frequency.

Vocabulary

If I give you any word, you can probably find several alternative ways of expressing that meaning. “big”, “tall”, “large”, “spacious”, “gigantic”… they all have different connotations, sure, but in the end they’re all descriptions for roughly the same thing - objects which take up a big fraction of your field of view when near them. Meanwhile, many conlangs will have a dictionary entry like gwop adj “big” and that’s it. Adding synonyms, especially ones with subtly different meanings allows you to greatly affect the way texts read (in a positive way).

At the same time however, often complicated words are derived from simpler concepts. This naturally has the effect of making them longer, causing a variation in the lengths of words - many short words with a few longer ones in-between is a common pattern. But if you simply create a new root every time you make a word, you won’t get that - and your hypothetical speakers will have to remember every single word without help, even ones they barely ever use.

I could go on and on and list things in every category of linguistics I can think of, but in the end it all boils down to this:

Irregularity in languages either preserves older, then-regular systems in now untransparent ways (English verbs are another great case study for this) or are the creation of sound change messing with regularity. The former is the reason why common words tend to be less regular - if you commonly hear a word it’s easier to preserve its original form and remember the irregularity once it has arisen. In the case of Navajo I mentioned above, curiously it seems to be that first sound change caused irregularity, and then the native speakers applying analogy caused the whole system to become even more irregular. See the paper I linked above for some hypotheses on how that worked.

Now, onto the actual question: Assume you have a conlang already, and it lacks history and is entirely too regular. “Sterile”, one might say. What can you do? I’d like to present you two options:

Invent a history for your language. Sketch out how your verbal system may have looked in the past and see if you can lead that to some interesting irregular forms or alterations. Come up with some sound changes that may have led to the current state of the language. You don’t have to do this in great detail, but obviously (as always with conlangs) the more effort you put in, the better it will look.
Make your language the history. If you don’t mind your end result potentially looking vastly different from what you have now, you can decide to move the  current state of the language into the past. You may have to make some changes to vocabulary to keep it in line with technology, but otherwise there’s not really any difference between a modern language and a “proto-language”. Then, you can track its changes through history in great detail, and in doing so introduce its natural flavour. No one has to know that the proto-language you worked from was unnaturalistic (but you’ll have to live with that knowledge. Just remember that you have to start somewhere, you can’t derive every conlang from the first utterances of mankind).

As a footnote, I’d like to make a book recommendation: The Unfolding of Language by Guy Deutscher. In this book, Deutscher discusses (in a very accessible manner) exactly what this question boils down to: how and why did languages become the way they are - messy and irregular and oh so complicated. I believe every conlanger should read this book, regardless of level of experience.


International Auxiliary Language created by a Japanese person

Assuming that the OP misremembered a few facts, the language may be Babm, invented by the Japanese philosopher Rikichi [Fuishiki] Okamoto (1885–1963) and first published in 1962. It uses the Latin script as a syllabary (which is not the same thing as using a latinate vocabulary) and has "some degree of analytic inflection".


Consider an isolated, close-knit community; which characteristics is their language likely to have?

Derek Bickerton and John McWhorter both have studied pidgins and creoles. A general observation is that communities that have to deal with other communities who don't speak their language, but still have to communicate resort to using pidgins, creoles which are simplified, grammatically speaking. McWhorter says English lost it's complex grammar when Vikings arrived and couldn't deal with the complexity.

On the other hand, island communities that don't have to deal with other people can tolerate arbitrarily complex grammar since children have a spectacular skill for acquiring their first language as compared to adults. So as an isolated language accumulates difficulties, there is no pressure to make them go away, they just get added to the pile of obligatory complexities.

Another feature of Island speakers in specific is they are more likely to use a "towards the shore/away from the shore" as a grammatical marker, ref "When "North" Isn't Actually North: Geocentric Direction Systems"

EDIT:
Large phoneme inventory. Chinese, a lingua franca has a small inventory and a small inventory of syllables. Rotokas has a small phonetic inventory. Someone would have to graph this to see if there is a weak relationship.

Inflections (really, any morphology), irregular forms (lexicalizations), culture-specific complexities-- I'd predict more of all of these for an isolated language. Proving it to satisfy skeptics would take a few academic papers. English's "2nd cousin twice removed" system, is complicated, but English is a lingua franca. Hard to say beyond generalities.


You seem to be confusing sounds with their representation in writing; similarly, countries and languages are not equivalent either.

There is an inventory of sounds that are used in human languages; though most languages only use a small portion of it. If you are aiming for an international language, you should probably select those sounds that are common to most or all languages. I believe that toki pona comes close to that.

Representing these sounds in writing is a completely different matter. Because different languages use the same letter to represent different sounds, your best bet might be to make up a completely new alphabet; then you don't have any pre-conceived notions of pronunciation to struggle with. On the flip side, everybody then has to learn the letters and how to pronounce them, which makes your language harder to learn.

In your question you also touch on morphology: that is a whole different field, which you should probably put in a separate question.

So, to summarise:

each language has an inventory of sounds it uses, these are called phonemes.
phonemes are represented in writing by letters; this is not a 1:1 mapping, and also
depends on accents and dialectal variation.
Letters can have diacritics (such as the dots on top of the ü) — these usually make them separate letters from the base form.
the letter-phoneme mapping is arbitrary; there is nothing inherent in the letter that determines how it should be pronounced.

In general I would recommend that you read up on some of the concepts of linguistics, as that would make it easier for you to express what exactly you want to achieve.


How many unique sounds does the average conlang have?

Depends what you want to do. If you want to be able to emulate all the words of real languages, add the whole IPA system. If you want nice melodic options, add in accordance with your preferred music system (Asian 5 tone, Western 7 tone, Modern 12 tone, each with steps and variations, and repeating form 20 Hz up to 20 000 Hz) and for each possible sound humans can produce - different voiced and voiceless sounds, whispered (ha) or normal (a), and so on. If you want to actually use it and keep it independent of other languages, I suggest keeping it simple - a movie language, for instance, is more effectful if you only choose in-character sounds.

Btw, you get a lot more sounds even in English and Italian if you include unusual words, regional dialects and so on - a large part of the IPA phonemes can be used in either language, though people often don't notice.

Here a few different English vowels (all mainstream):

Hut
Hat
Heroic
Hellenic
Hmmmh
Hit
Here
Hot
Hotel
Herd
Hoover

Alpha
And
Entity
About
e-in-Garden
India
Equal
Oven
Organ
Earth
Ultra

Iron
Out
Able
Oil
Over

Hi
How
Hey
Hoist
Holy

That's 32 distinct sounds. Some might be debatable, they are also dependent on dialect - "and" and "entity" start with the same sound for some, but I hear a difference - at least in some regions. The e in "Garden" isn't a sound at all according to some. And so on. The version on Wikipedia (English phonology) is slightly different. "Ha" is even in IPA written as two sounds, though it clearly is one sound (a whispered "a"), as you can see when stretching it, with or without adding a letter afterwards. I even ommitted a few vowels only the British/Australian/Canadian people use. According to Google, US English has 14-16 vowel phonemes, Australian English 20-21. And the whispered variety isn't even included.

If you multiply by three for tonal (add Up like we do in questions and Down like we do in some forms of emphasis or sounding defeated), you get 96. Asia also has a wavering tonal, but that can be emulated with two letters imo.

If you multiply by two for 2 different lengths, you get 192. If we ignore the h-sounds, we are still at 96.

So what you have is not that much.


Will I be able to read texts written in all Romance languages simply by learning Interlingua?

On their site it says:

Millions understand Interlingua "at first sight". Speakers of Romance languages especially understand Interlingua immediately and almost effortlessly. Ideal for traveling!

So it's the other way round: if you speak a Romance language, Interlingua will make sense to you because it contains many elements (eg vocabulary) from these languages. This does not, however, mean that you can necessarily understand any Romance language after learning Interlingua, though I assume there will be some benefit going both ways.


How many dialects of Tolkien's Elvish are there?

In this article, it is mentioned:

Primitive Quendian (language of the Elves in Cuiviénen)
Avarin
Various Avarin languages (some later merged with Nandorin)
Common Eldarin (the early language of all the Eldar)
Quenya (the language of the Ñoldor and the Vanyar)
Quendya (also Vanyarin Quenya) (daily tongue of the Vanyar: closest to archaic Quenya)
Ñoldorin Quenya (also Exilic Quenya) (the "Elven Latin" of Middle-earth)
Common Telerin (the early language of all the Lindar)
Telerin (the language of the Teleri who reached the Undying Lands)
Nandorin (languages of the Nandor — some were influenced by Avarin)
Original language of Greenwood the Great
Original language of Lórinand
Sindarin (language of the Sindar)
Doriathrin (dialect of Doriath)
Falathrin (dialect of the Falas and Nargothrond)
North Sindarin (dialects of Dorthonion and Hithlum)

So a good many dialects exist. However, we cannot exactly count how many there are, because it mentions "various" and we don't know whether there is a hierarchy of languages that have branched off somewhere else.  However, we can confirm there are at least 17 dialects of the Elvish.


Dropping words happen (the ne of negation notoriously drops pretty systematically in spoken French) and commonly a that, as Gregory points out. However, I believer a true "silent word" is a nonsensical concept.
For starters,  Silent letters are historical artifacts of a writing system. They are not a feature of the spoken language, so right there, a "silent word" cannot be something that happens in the spoken language unless the words in question are composed of phonemes or features that are merely difficult to hear from locutors of a different language. Still not silent in their native language. If a writer writes down a word, they typically do it with some sort of communicative intent (even if not consciously so).
Second, in the spoken language, something that isn't pronounced in one way or another literally doesn't exist by definition (we can argue about stuff like sandhi and the side effects of sound change, but that's beyond the scope of this discussion IMO).
So unless your language has a need to transcribe something that is literally not said (and we usually have punctuation and emoticons for that), then a "silent word" is, in my opinion, a self-contradicting concept.


Is the language of The Gostak more than just relexified English?

Well,

it is pretty clear that this is just relexified English, just look at the function words: at, the, of, where, but, is, with, .... Also the syntax is 1:1 English syntax, and even the inflections (plural in -s, perfect participle in -ed, third person singular present tense in -s) are the original English one. All in all, it sounds like a strange kind of English slang.


I think you're conflating a/o confusing a couple different things here.

First, "cutter" is not "instrumental". (At least in English!) In English grammar, -er is (among zillions of other uses) the morpheme that indicates "agent noun"; so, cutter means "thing that cuts". It is the actual agent by which cutting happens.

The Instrumental Case is a grammatical function that indicates the means by which the agent or subject of the verb does the action:

I-subj cut-verb the.box-obj (with.a.box.cutter)-instr.

If English had case endings like Latin, you could see the difference easily:

Puer-NOM cistam-ACC cultello-ABL secavit-VERB

Latin uses the ablative case to denote the instrumental case, due to ancient case syncretism of the old ablative, locative and instrumental cases.

-ise / -ize, in English, is a grammatical morpheme that indicates the word is a denominal verb. This means that the verb in question is made from a noun. We already know that English weirds. It verbs nouns at the drop of a hat.

I will hammer him if he attacks me with the knife.

Your example, "I will hammerise him if he attacks me with a knife", doesn't actually make sense in context. This is because -ise doesn't mean "use something as an instrument", it means "turn something into something else".

Immigrants ought to be Americanised through educational programmes.
The machine pulverises large pieces of stone into gravel.

I think your best bet, as far as "converse" of or "opposite" of the instrumental case, would be the

noninstrumental case, which I just made up.  It does what the instrumental case does, only in the other direction. Essentially, the speaker denies the instrumentality of the named article.

Puer-NOM cistam-ACC cultellei-NONINST secavit-VERB

I considered "deinstrumental", but that's already a thing (a noun or verb made upon an instrumental form).


Are there convincing examples that auxiliary constructed languages are in fact easier to learn?

Some auxiliary languages are easier to learn than natural languages. There have been many experiments that show that Esperanto is both easier to learn than other languages, and also makes learning future languages easier.
Two quotes from some of the experiments on Esperanto:

"It is possible for the average student to understand written and spoken Esperanto in 20 hours better than he can understand French, German, Italian, or Spanish after 100 hours."
"A child can learn as much Esperanto in about 6 months as he would French in 3–4 years... if all children studied Esperanto during the first 6–12 months of a 4–5 year French course, they would gain much and lose nothing."

However, it's not necessarily true that auxiliary languages are meant to be learnt faster than natural languages. Esperanto is a very regular language, and that makes it easy to learn. Other languages, such as Interlingua, are not as easy to learn, but are meant to be more recognizable to someone already familiar with the vocabulary of Romance languages. It is still more regular than the natural languages it's based on, so it likely is easier to learn, but it sacrifices some regularity in order to have a more familiar vocabulary.


Is it attested for noun classifiers to be coopted for directionality?

Such a system is indeed attested! And not only that, it’s actually surprisingly common. Usually the category is called andative and venitive, for ‘going’ and ‘coming’ respectively (though I prefer ‘translocative’ and ‘cislocative’). Here’s an example from Komnzo (Döhler 2018):

Yfathwroth.
They hold him away.
y-          fath     -wr -o   -th
3SG.MASC.α- hold.EXT -ND -AND -2|3NSG

And one from Lucas Quiaviní Zapotec (Oto-Manguean, Anderson 2017):

Rata rsily rityug Lia Petr gyia.
Every morning Petra goes and cuts flowers.
rata  rsily   r-  i-  tyug Lia  Petr  gyia
every morning HAB-AND-cut  Miss Petra flowers

Many languages have even more elaborate systems, distinguishing many different directions beyond just ‘coming’ and ‘going’. For instance, Yagua distinguishes ‘upriver’ and ‘downriver’ directions (Payne 1997):

Sąąnaa suutiimuníí.
Wash him/her downriver.
sąąna -a   suuti -imu -níí
2DL   -IRR wash  -DR  -3SG

While Southern Pomo has an exceedingly large array of around 15 directional suffixes, which may be applied to verbs of motion (Walker 2013):

ʔapʰ꞉alméčʼin
climb down from above
ʔapʰː -alamečʼ -Vn
carry -DIR     -SG.IMP


How can I make my conlang's borrowings naturalistic?

Should I destlangize the word, or leave it in its “native” form?

In natural languages, borrowed words are almost always "destlang-ized" to some degree, but it won't necessarily always to the same degree. Even within the same language, often some borrowed words will be more integrated into the language than others. The more recently a word was borrowed, the more speakers of the language will treat it as a "foreign" word and be willing to make exceptions for it, but as its use becomes more and more common, speakers will inevitably begin to treat it as a native word if it doesn't fall out of use.

Does the borrowed word take on the conjugation/declension pattern of destlang?

Sometimes, sometimes not. There are examples of both in natlangs.

The English verb "to google" has been borrowed into many languages, and it seems to typically conform to the conjugation patterns of those languages. Even in Japanese, a language with a famously closed class of verbs, borrowed "to google" as a verb ググる(it may have become a verb after being borrowed as a noun, but either way, it's quite remarkable).

Yet it's also possible for exceptions to be made. This happens with some English noun borrowings (most English speakers won't try to pluralize edamame or Pokémon with English plural morphology), but not with others (many English speakers will pluralize zucchini as zucchinis, and you'll pretty much never heard zucchino).

In my experience, verbs are more likely to take on the native conjugation patterns than nouns are native declension patterns, but I don't have any data to back that up cross-linguistically. A borrowed word is definitely more likely to be conjugated or declined like a native one the longer it has been in the language (the pedantry about pluralizing Latin borrowings in English is an exception to this, but that's more because of the social prestige associated with having studied Latin).

Does the borrowed word get re-spelled to conform to destlang’s orthographical conventions?

This really is a case-by-case thing. If the language uses a completely different writing system, almost definitely, but sometimes the orthographical conventions won't be the same as native words. Japanese uses katakana for borrowings, for instance, and English borrowings from Japanese and Chinese tend to follow whatever romanization scheme was most popular when they were borrowed, even if the pronunciation is pretty opaque. For instance, the Chinese word 道 was borrowed as "Tao" in English based on older Chinese romanizations, even though the Chinese word now romanized as dào and the English derived word "Taoism" is more often pronounced /ˈdaʊ.ɪzəm/ in English (though a spelling pronunciation /ˈtaʊ.ɪzəm/ has arisen due to this).

Does the borrowed word’s pronunciation get changed to conform to destlang’s phonemic conventions (e.g., elimination of consonant blends, all syllables must end in a vowel, etc.)?

Almost always yes. While sometimes educated speakers or upper-class speakers will try to pronounce a borrowed word with its "original pronunciation" rather than its borrowed one ("gyro" is a good example of this), even those pronunciations are almost always somewhat changed to fit the destlang's phonology better, and often they aren't even closer to the pronunciation in the sourcelang. How exactly the word is altered to fit the destlang's phonology depends on the particulars of the borrowing situation, however.

What sort of methods exist for choosing which words to borrow? What causes a “native” word to fall out of use in favor of a borrowing, or, contrariwise, why would both the “native” word and the borrowed word stay in use?

I've combined these questions because I feel there's a lot of overlap in the answers. Often, words are borrowed to fill a semantic gap in the destlang, which is why words for new technologies are so often borrowed (think of how many languages borrowed the word "television"!)

Borrowings are also often used to refer to the "versions" of certain things from the part of the world that speaks that language -- consider how anime, a generic word for all animation in Japanese, was borrowed into English as a word for a style of Japanese animation, or how English borrowed "chai" from the Hindi/Urdu word for tea, चाय (cāy) / چای (ćāy) to refer to tea with certain spices based on Indian recipes.

Also, sometimes words are borrowed because they carry some social value seen attractive by the speakers of destlang. Maybe destlang speakers think sourcelang sounds refined and sophisticated, and so upper-class destlang speakers borrow words from sourcelang to sound fancy. Of course, this sort of situation depends on a lot of social and sociopolitical factors wherever the languages are spoken.


What is a realistic *upper bound* on the complexity of nominals that can be incorporated into a verb?

Part of the confusion here is that the loss of the grammatical markers you note are a logical consequence of the the semantic use of incorporation.
An incorporated noun may be best compared, in my opinion, to a nonfinite verb, which will also typically lack much of the morphological features of a normal verb. This alone makes it evident why the standard markers a noun may present will usually be absent. Marianne Mithun describes four major reasons to incorporate a noun (quoting summary from Rosenfelder, Advanced Language Construction, pp. 182-184):

Narrow the focus of a verb by adding some sort of descriptor to it. You may want to incorporate tools, for example. In Nahuatl, such incorporation often translate to "X like (a) Y(s)".

Allow an otherwise oblique argument (usually of a semantically, if not syntactically labile verb) to become its subject (cf. English, "My head aches" vs. "I have a headache").

Background an argument that has already been mentioned.

Adding a classifier of some sort. This is an integral part of verbal morphology in the Algonquian Languages, for example. Chinese also does it to create suppletive forms of single-syllable verbs that may be highly polysemous or homophonous.

Add to this the fact that in most languages, you cannot incorporate the subject noun of an unergative verb (probably no language at all allow it, but I haven't looked into it in details), it is easy to see why incorporated/nonfinite nouns have little need for all the bells and whistles of regular arguments: you are either generalizing or backgrounding the noun, so you don't want or need to add these syntactic elements.
Regarding possessive markers specifically, I should point out that even in languages without incorporation, possessive markers are liable to be dropped if the possessor is already a separate argument in the sentence: I stole money from him, It struck him on the nose, J'ai mal à la tête, Je lui ai cassé le bras.
Finally, if a language has incorporation, it is usually rare for it to have a fully separate word category of adjectives as we understand them to begin with! In many of these languages, adjectives take the form of descriptive verbs or adjunct nouns that can themselves be incorporated into themain noun (cf. English Bluebeard, whiteboard, blackbird...), and syntactically, it doesn't typically work to incorporate an entire relative sentence.
However, some languages, such as Chukchi do allow for the whole noun+adjective phrase to be incorporated, and quite a few languages allow for numeral markers to be incorporated, although this is actually part of the verbal paradigm itself i.e. if you incorporate "I saw two persons" you are incorporating the noun "person" to a verb root that means "see two X", not incorporating "two men". That's what happens in Southern Tiwa or Algonquian languages (Nishnaabemwin: Giibimdaaswishiniizhdaabaan’gizwag, "They came in twelve carloads").
So, in summary, I would say aside from adjuncts noun and adjectives (which itself would make your language unusual, though not outside the realm of human experience), any other grammatical attribute of the noun you want to "incorporate" you should do so as an integral part of you verb paradigm, not as part of the incorporated root per se. If you are seeking a language that looks as natural as possible, anyway.


What is the influence of Russian on Tolkien's languages?

To begin with, Tolkien writes in letter 142 that

  I love music but have no aptitude for it [...] Slavonic languages are for me almost in the same category. I have had a go at many tongues in my time, but I am in no ordinary sense a 'linguist'; and the time I once spent on trying to learn Serbian and Russian have left me with no practical results, only a strong impression of the structure and word-aesthetic

which implies that large portions of his languages are probably not structured on Russian. I then further point to this essay. In summary, the

  conclusion that Tolkien “consciously or unconsciously achieved a literary effect in terms of Slavic culture through the prism of the Germanic”, goes too far on too little evidence [...] Better would be to say that Tolkien did indeed incorporate a few Slavic elements into the multifaceted and multi-sourced structure and background of Middle-earth, but that he did so quite sparingly and, in almost every case, only at its furthest margins.

While the detailed analysis can be found in that article, it seems fairly clear that while a few words may have crept in here and there, these words were also Germanic cognates or were cut out of Tolkien's language, with only one or two exceptions.


Has any conlang ever replaced the use of a pidgin?

Basic English is minimal in that it limits the number of words in the language (though not as extremely as Toki Pona). It was intended to be an international auxiliary language (although it never really caught on).

The language was used in 1945 in order to quickly teach Chinese sailors to understand naval orders. This was reported at the time in a Time magazine article (paywall beyond first two paragraphs; the reference to the article comes from Wikipedia).


How does the Wede:i language reflect their cultural focus on government?

I don't think you can generally assume a strong correlation between the vocabulary of a language and culture of the kind you are asking about. Just like the "50 Eskimo words for snow" is a myth, it would also apply to other languages...

Not knowing the language in question I would think that there is a cultural influence, but not as obvious as having more words in a given topic area. I would expect a fine-grained system of honorifics, expressed in, for example, different verbal affixes depending on whether you speak to someone who is superior to you or not. So you express respect by using a different form of the verb, but not a different lexical item.

The same would apply to other areas of discourse. Politeness markers, modality (should, could, would,...) all play a role in social interaction, but do not necessarily manifest themselves directly in the vocabulary.


Sona: how complete it is and how alive it is?

I think it's pretty much dead.

There is~was a Yahoo group. It has 80 members and no recent activity. But Yahoo groups are all screwed up now, so it's difficult to tell.

There is a dead Sona forum with 14 members. There are a couple translations. No activity since 2010.

There is a dead Sona twitter feed with 13 members. No activity since 2013.

There is a dead Sona tutorial website archived by the Wayback Machine. Not reachable by ordinary means.

The grammar book was hosted online in a now defunct location archived by Wayback Machine.


What is reduplication used for in natural languages?

WALS Chapter 27 describes a number of functions for reduplication. All examples below come from chapter 27 unless otherwise noted.

On nouns

Pangasinan uses reduplication to mark plurals:

báley "town"
balbáley "towns"

Ilocano uses reduplication on nouns to mark a distributive plural:

sábong "flower"
sabsábong "various flowers"

Ilocano also uses reduplication to turn nouns into reciprocal verbs:

bales "revenge"
balembales "to avenge each other"

Chukchi uses reduplication to mark the absolutive case:

jokwat "eider duck"
jokwajow "eider duck (ABS)"

Kayardild uses reduplication to turn nouns into adjectives:

kandu "blood"
kandukandu "red"

Yawelmani uses reduplication to mark associatives:

k'ɔhis  "buttocks"
k'ɔk'ɔhis  "one with large buttocks"

On verbs

Luiseño uses reduplication to mark the number of an inherent object:

lawi "to make a hole"
lawlawi "to make two holes"
lawaláwi "to make more than two holes"

Mountain Arapesh uses reduplication to mark carelessness on the part of the subject or agent:

su "to touch"
susu "to touch all over"

Luiseño also uses reduplication to turn a verb into an adjective:

lepi "to tan, soften"
lepélpiš "pliable"

Ancient Greek used reduplication to mark the perfect aspect (Ancient Greek Press Book Chapter 42):

γράφ "write"
γέγραφ "have written"

Tigak uses reduplication to turn a verb into a person who regularly performs that action:

giak "send"
gigiak "messenger"

On Adjectives

Turkish uses reduplication to mark intensity:

beyaz "white"
bembeyaz "very white"

Automatic Reduplication

Additionally, automatic reduplication is possible, where an affix requires reduplication of the root with no additional meaning. Chapter 27 gives this example from Ilocano:

singpet "behave" + agin-
aginsisingpet "pretend to behave"


How to link extraterrestrial animal names from other language with terrestrial languages?

I think, the more generic a term is, the better you can use a known term in your native language. The more specific a term is, the greater is the need for some circumlocution or some conlang term.

Examples: Specific kinds of flowers and trees in Tolkien's "Lord of the Rings" have constructed names like mallorn, niphedril, or simbelmyne. He consistently used pipe-weed (the word tobacco is used by the narrator, but not in dialogues). Already on the level of genera, Tolkien uses terms like pine tree, oak, ... and of course there is grass, there are trees, there are horses and so on.

Whether you want to call some space creatures "cows" depends on the picture the word "cow" evokes and the uses of cows (Do they give milk and flesh? Can you use oxen for ploughing or driving a cart?) in your fictional culture.


Indeed, there doesn't seem to be any canon word for "skull" in Klingon, so a compound should be fine.

Note, however, that some compounds are constructed without separation between their parts (see for example Wiktionary's list of Klingon compound words) with no apparent rule as to why, so "skull" could conceivably be nachHom.

BUT, since -Hom is also the diminutive suffix, nachHom would primarily mean "little skull", making nach Hom is the less ambiguous translation.


Are Esperanto's part of speech endings actually beneficial?

For those unfamiliar with Esperanto POS suffixes,

-o noun
-i verb (infinitive)
-a adjective
-e adverb

For example:

sano - health
sani - to be healthy
sana - healthy
sane - healthily

Since Esperanto has free word order, having POS markers allows the differentiation between the following phrases:

ĝoje knabino ludas - a girl plays happily
ĝoja knabino ludas - a happy girl plays

Esperanto and LFN have a very similar affix system, however unlike LFN, Esperanto root words have no innate part of speech, so there is no way of "adding" a verbal suffix to a noun or an adjective. Rather, you would be changing the nominal/adjectival suffix to the verbal one and forming the verb based on the root word. Knowing the POS of any given word makes understanding unfamiliar words a lot easier, which is very advantageous for an auxiliary language.

With that being said, in EO poetry, nouns often drop their -o ending for aesthetic reasons.

  Berlino sen vi estas urb' (urbo) sen harmoni' (harmonio)
  Estas trista, trista, amasloĝej' (amasloĝejo)

Between EO and LFN's, there is no "better" affix system. They are just two different ways of doing the same thing.


Why are sign languages considered to be natural rather than constructed languages?

The history of sign languages is more akin to that of creoles than that of a constructed language which later gained native speakers. Consider the following two examples:

The grammar of Esperanto and a large chunk of its vocabulary was created, codified and written down by L. L. Zamenhof. People who were interested learned his language according to his rules and later passed it on to their children, creating the first native speakers of it.

The development of Tok Pisin is described as follows: Contact between English speakers and locals of Papua New Guinea gave rise to a pidgin, an incomplete and bare-bones not-quite-language that was just good enough to communicate - everyone would have spoken it a bit differently at that point in time. It became used more commonly and was passed down as a native language to children, creating a full-fledged language. At no point however did its speakers sit down and decide on what grammar Tok Pisin ought to have.

Now compare these with the case of the Nicaraguan Sign Langauge, the currently only natural langauge which we have actively seen develop. Deaf children of Nicaragua previously communicated with the people closest to them with improvised home signs and gestures (in other words they had at best something akin to a pidgin). When they were brought together in a new school for the deaf, they had the need to communicate with each other. The school encouraged use of mouthing or fingerspelling Spanish, but the students, who were not native speakers of Spanish failed at learning these skills. Instead, they started communicating by using their own home signs, forming a pidgin that developed over the following years and was taught to younger students who later arrived. Over time, the language developed complexities similar to what you would find in other signed languages - evidence that it had developed beyond the initial pidgin stage.

It is clear that the example of Nicaraguan Sign Language is much more similar to that of Tok Pisin than that of Esperanto.


Are constructed languages intellectual property? Do they ever stop being IP, once people use them?

The short answer is that there are no mechanisms in place by which one could credibly copyright, patent or otherwise secure ones language. Works you create about the language (such as a grammar document or a poem) of course fall under the same copyright laws as any other works of their kind and as such generally belong to you, but your language as of now is just as copyrightable as English.

For a long answer, I recommend watching this talk by Sai (founder of the LCS) about exactly this topic.


An unordered set of potential reasons:

Showing off. I know something cool that you don’t. For some, that is the reason to learn Latin but for others that may be the reason to attempt to learn e.g. a language from the Lord of the Rings. It can easily have a vast impression on fans of the franchise.
Cosplay. This is especially true for languages appearing in games/movies/etc. For many cosplayers, the prime goal when cosplaying a character is to mimic them as perfectly as possible. Of course, if you’re mimicking e.g. Eragon after he has learnt the ancient language, you want to at least be able to produce meaningful sentences (unless you’re explicitly aiming for mishaps like the one in the underground city — but arguably that requires even more knowledge). If you’re cosplaying Arya, that is even more true.
Creating a franchise that uses a conlang. If you want to make extensive use of your conlang while writing a series of books like A Song of Ice and Fire, getting it right at later stages is much easier if you have some basic understanding early.
Just because they can. For some people, picking up a language is extremely easy so they may just want to do it for intellectual stimulation.


Is there a stroke order for any of the Klingon alphabets?

There have been stroke ordering proposals by fans devising handwriting of pIqaD. One is http://klingonska.org/writing/examples/pic/zrajm-piqad.jpg , from  Zrajm of Klingonska Akademien: http://klingonska.org/piqad/. Another had been proposed by the late Glen Proechel's group:

  Interstellar Language School (lead by Glen F. Proechel) has published “An Alien Writing System Primer” explaining how to write pIqaD in longhand. (It is non-canon, of course – and to my knowledge not endorsed by the KLI.)

It was 20 years ago, I've seen it, and I don't remember it. (I do remember not liking it. ;^)


Would these features be naturalistic in this scenario?

Yes, the whole thing looks naturalistic.

ad 1) When you assimilate the Old Norse words to a Goidelic phonetic system, lenitions and broad/slender distinctions come in very naturally. It will be more difficult when you insist on some Old Norse sounds sticking out of the Goidelic system; they can form exceptions to the lenition rules or evolve specific lenitions of their own.

ad 2) Retaining the Old Norse suffixed article is definitely an option, and simplifying it to only one form (independent of gender, case, and number) looks most natuaral to me, but keeping the inflected forms is also covered by your artistic license as a conlang author. Or you may inflect the definite forms according to Goidelic inflectional rules.


One guy taught his daughter Volapuk.

There is a contemporary case of someone teaching their kids their personal conlang, she used to be active on one of Facebook's conlang groups.

The revived languages, Cornish, Hebrew, Sanskrit, have similar dynamics to conlangs. Having government support in the form of schools and day care works wonders for the project being successful.

Getting a child to speak your languages takes time (20+ hours a week) of exposure, and it really helps to have a community of peers who also speak that language, or a child's decision to keep using their parents language will be personal and idiosyncratic. I get this impression from people I've met who tried speaking Arabic or Icelandic to their kids in the US where they got plenty of exposure to their parents, but no particular supporting community of peers.


It might be sona ijo tawa —knowledge of moving things— or sona ijo ante —knowledge of things that change.


How would I make an efficient, written, language while still providing the least ambiguity that is reasonable?

First a in this form brand new fact from natural languages: All natural languages are of approximately the same efficiency despite their quite noticeable differences (some languages are spoken at a rather fast pace in syllables per second, but than the information content of a syllable is lower than in other languages that are spoken more slowly). The reference is Christophe Coupé, Yoon Oh, Dan Dediu, and François Pellegrino, Different languages, similar encoding efficiency: Comparable information rates across the human communicative niche and they give a value of 39 ± 5 bit/s.

So you can expect that a naturalistic constructed language will fall in about the same range; maybe somewhat less efficient, because it is difficult to get things just right by construction that have been optimised by language evolution over a long time.

For completely symbolic languages, look up the term pasigraphy and take a glimpse on some systems that have already been invented.


What are language concepts that could be considered to be based on human anatomy?

Some obvious ones:

Phonetics, be it of spoken or signed language, is obviously constrained by the body of humans - both in the channels (aural, visual) employed and also in how they are employed.

Metaphors often make use of body parts. Spatial prepositions and adverbs are often derived from relevant body parts: front from face, forehead, nose, chest; back from back or butt; up from head… you get the picture. Basically every organ has been referred to as being the cause of emotions etc as well in metaphors.

Words for directions in particular are also somewhat based on human anatomy. We have lateral symmetry (left-right) but an alien could likely have some form of radial symmetry in their bodies, which would make the concepts of leftness and rightness very weird to them. Aquatic beings would also likely have a different concept of directions altogether, probably based more on the orientation of their own bodies than relative to the ground.

Those are the things that come to mind. However, much more importantly, the inner workings of language as a whole would likely be different from a human’s. There are some things in human language that you really wouldn’t assume to be necessary. Just to make two examples:

It seems pretty clear that humans take the raw audio input, break it into segments (phones) then further abstract those phones into phonemes, which are then in turn used to build more complex words. One could just as well imagine skipping the segmentation step and going directly from audio to meaning. There appears to be evidence however that some songbirds also employ what could be considered phonemes in their songs, so perhaps it is to be expected.

Another thing is in syntax: human language does not appear to allow circular dependencies, that is word¹ A modifying word B, which in turn modifies word A again. From my fairly limited understanding of syntax, human sentences can be structured in a tree structure. It seems plausible that an alien language might have more or less freedom, perhaps allowing cyclic graphs in their syntax… or in the other direction, only linear dependence. An example of an alien conlang playing around with this is Europan, which I personally consider one of the most interesting conlangs I’ve ever encountered.

¹or clause


Can you construct garden path sentences in Lojban?

Lojban's official formal grammar is written in YACC, which is a LALR(1) parser generator. Since this means that the parser only ever "looks ahead" a maximum distance of one token while parsing, garden path sentences are impossible in the traditional sense.

This just means that the parse tree can't be drastically transformed during the sentence—it doesn't mean that the meaning of sentences can't be changed signficantly later on within them. The first example that comes to mind is the song NA KU from Djemynai's ZA'O, which contains the chorus "pu ku zvati fa do .ije ca ku zvati fa do... na ku." This glosses roughly as follows:

pu-ku zvati   fa-do
PST   present 2sg.NOM
You were here.

.i-je ca-ku zvati   fa-do   na-ku
and   PRES  present 2sg.NOM NEG
Now you are not here.

Note that the use of ku allows the negation particle to be moved to the very end of the sentence. This does not affect the parse, so it's not a traditional garden path sentence, but it still allows the creation of a surprising effect, which is similar in some senses.


Are there works composed in Quenya or Sindarin by people other than Tolkien himself?

Attolma
Poems in Quenya
Some more poems in Quenya
Pater Noster in Sindarin
Poems in Sindarin

NB: I am not competent to guarantee that any of these works are "correct" or "grammatical".


Why do I have such a problem with my conlangs being ugly?

What you need is to adjust your phonotactics. Since you mention it in your question you apparently know what they are, but you aren't using them to get the sounds you want.

You say you find "tais" to be hideous, but you don't explain why, so let's say you don't like the way that a diphthong sounds in a closed syllable. (If this isn't the case, take this as an example for whatever the problem is.)

Once you've located the problem, you have to determine how to eliminate it by making rules for new phonotactics. You can think of lots of ways:

The diphthong becomes a monophthong: tais > tas,  tis or tes in a closed syllable (tas might be problematic since it creates ambiguity with the singular). Or, alternatively, two monophthongs: tais could be [ta.is] instead of [tajs]
A new consonant could be placed to separate the diphthong: tais could transform into tayis, maybe taus could be tawus (based on a simple rule of adding y before a front vowel and w before a back vowel)
The diphthong could monophthongize and simple color the next consonant: tais could be pronounced [taɕ]. You could create a pattern with other consonants, e.g. tait > [tac], taid > [taɟ]
Even if some of these options are problematic in your case (maybe you don't want to "contaminate" your agglutinative language), you could still retain the phonemes /tajs/ and just have some of these options as allophones of it (so e.g. [e] or [e:] could be an allophone of /aj/ in a closed syllable, [ɕ] could be an allophone of /js/)

What you need to do is just determine what sounds ugly to you and create phonotactic rules that cover whatever the problem is.


Can programming languages be categorized as conlangs?

No. "Constructed languages" on this site refers to artificially created languages for intelligent beings, not machine languages. In the absence of another qualifier a "language" is, as I wrote on another site, a system for communicating propositional and conceptual information to other beings. This is different from communication. Programming languages can definitely be used to communicate - and they carry meaning - but that doesn't make them languages. Purely referential communication (using symbols to directly refer to things in the world without metaphorical extension) is not enough to be a language, language must be able to communicate abstract concepts that are beyond any sensory or referential basis. Programming languages are systems for encoding instructions for machines, and not general purpose concept exchange systems.


With the death of CSUR, has there been any new Unicode proposal for con-scripts?

There exists the UCSUR (Under-ConScript Unicode Registry) which was created as a sort of temporary holding place for proposals to avoid conflicts until the CSUR is once again active.


How much Dwarvish did Tolkien actually devise?

As per this (cited by "An Analysis of Dwarvish" in Arda Philology 1: Proceedings of the First International Conference, with a very nice glossary of the language, which can be found here):

  Regarding Khuzdul, Tolkien stated that "this tongue has been sketched in some detail of structure, if with a very small vocabulary" (PM:300). It evidently came into being in the thirties.

Here PM refers to the Peoples of Middle Earth. The complete corpus of the language is described on the same site as being

  a few names, like Khazad-dûm and Zirak-zigil, the inscription on Balin's tomb, and a battle cry: Baruk Khazâd! Khazâd ai-mênu! "Axes of the Dwarves! The Dwarves are upon you!"

A petty-dwarf, Mîm, is also named, in The Children of Hurin, though that is the only reference there. The names also include Chamber of Mazarbul [records].

(A complete glossary is given on the website; it is too long to copy here.) It also mentions Appendix D, E, and F in the Lord of the Rings (F primarily containing history, of course) and the Appendix in the Silmarillion also apparently contains a reference to Khuzdul:

  At least one Khuzdul word made its way into Sindarin: kheled "glass", that appears in Grey-elven as heledh (see the Silmarillion Appendix, entry khelek-)

This appears to be all we know of Khuzdul. In spite of this, extensive analysis has been made, with a not insignificant amount of it guesswork. See "An Analysis of Dwarvish" for one example (provides a theory of language structure).

Of course, Tolkien did state that it was "sketched", but the question is where it was - there's a chance it may be unpublished:

  Yes, there is some unpublished material concerning Khuzdul. However, it’s only a small amount, and as I recall, it consists mostly of phonological discussion, though inevitably there is in conjunction with this some discussion of the grammatical significance of various root modifications. But don’t expect anything like Etymologies or the "Early Qenya Grammar" for Khuzdul.


Why is the Lord's Prayer so common as a translation?

It is a long standing tradition to use the Lord's prayer as a sample text for illustrating natural languages, for instance, the mid-16th century Cosmographia by Sebastian Münster contains the Lord's prayer in Finnish as an illustration of the Finnish language.

It has the advantage of being available in many languages, including otherwise ill-documented or dead languages.

Its disadvantages are the religious bias and the fact, that some very marked constructions tend to occur in this text (in German, there is a relative clause in the second person singular ..., der Du bist im Himmel, ... a really rare beast).


Short answer: I've never seen or read a description of what you're seeking.

Long answer: What you're seeking is a most unlikely beast, reason being...

Generally speaking, auxiliary languages seek being completely or nearly completely a posteriori for reasons of simple expedience. Common design goals of an auxiliary language are ease of learning and simplicity of use.  These goals are best met when vocabulary and grammar are familiar to the target audience.  This is why Interlingua and Esperanto are considered "easy" languages to learn and have gained considerable user communities, with Esperanto boasting a small community of native level speakers.

What you're describing, a completely a priori invented language is most usually the domain of the artistic language, the engineered language and the philosophical language. With the exception of the philosophical inventors, most glossopoets are not interested in propagandising their languages as auxiliary languages.  Occasionally a philosophical language inventor will propose his language as a means of general communication, but this is usually done from a position of ignorance as to how language works (accomplished auxiliary language proponents are usually quite well aware how language works in the wild!).

Auxiliary languages tend not to be classified as a priori simply because they impose layers of difficulty that run contrary to the usual design parameters of the genre. However, it can potentially be argued that a priori invented languages can become auxiliary languages after a fashion and if the appropriate stars align. For example, it may be that Klingon has seen some use as an ad hoc auxiliary language if, for example, two groups of Star Trek fans who do not share a language in common other than Klingon happen to meet at a SciFi convention.

Needless to say, even if there were an actual auxiliary language that is classified as purely a priori, it certainly isn't famous. Otherwise, we'd know about it!


How could the future "Kesh" language from the book "Always Coming Home" by Ursula K. Le Guin develop from modern languages?

5000 years is a really long time for linguistic evolution, and after such a long time little resemblance between the original and the final outcome is left. So almost anything is a plausible outcome.
The feature "written language and spoken are completely separate things and are not interchangeable" has a nice scientific name alloglottography and it was quite common in the Ancient Near East. I wonder how it can survive in a society Ursula LeGuinn describes for the Kesh people because it is definitely harder to maintain than the knowledge of a simple alphabetic writing of the spoken vernacular.
The alphabet looks like a new invention but it shows some superficial similarities to Canadian Aboriginal Syllabics and may have evolved from them. Or it was just reinvented at some point of time after a period of illiteracy.


Are there any good programs out there to help when constructing languages?

Polyglot is a piece of software made specifically for the organisation, and management of conlangs as a whole. I haven't used it personally (preferring pen and paper to a large extent), but I've heard a fair few positive things about it.

Conworkshop includes a bunch of different tools for storing and organising things, but I've personally not found it particularly useful, and I have heard from people who have looked at the backend that you do not want to look at the backend, though I think they are doing a rewrite.

SIL Fieldworks is a vocabulary management program, and while developed for natlang lexicographers, it's also useful for conlangs. It's a rather powerful tool, but it has a significant learning curve to it. SIL also publishes other potentially useful free software such as Toolbox: https://software.sil.org/products/

Lexique Pro is a piece of software for making and editing presentable dictionaries. I haven't used it but it apparently offers compatibility with Fieldworks.

In addition to these, a regular spreadsheet program and a text editor can be quite useful, and there is a sea of both web and downloadable word generators (e.g. Gen, Awkwords, Lexifer) and sound change appliers (e.g. SCA2, GSCA), and for writing publishable materials, LaTeX, combined with a variety of packages for extra functionality such as Lingmacros and TikZ can produce fantastic results.


How much of Slovio is based on Esperanto?

In terms of the vocabulary, not much is based on Esperanto.

From the Slovio website:

  Esperanto? While Esperanto is a simple language its main problem is the fact that it is made up of too many unrelated languages and thus, if you speak Esperanto, no-one will understand you only other Esperantists. On the other hand Slovio, since it is made up of only closely related Slavic languages, can be put to an immediate use. Using Slovio, you will be understood by some 400 million people, most of whom have never ever heard of Slovio, but who will understand you.

So, it looks like the only inspiration Slovio has taken from Esperanto is the grammar.


what real world language does this look like?

Well, it looks like a sample of an English based creole language written down by an amateur linguist or a missionary in a private orthography. It looks like a first attempt on a writing system for a previously unwritten language, it does not look really ripe: Too many diacritics on the vowels, and some confusable diacritics, too, e.g., á, à, ā, ȧ, what do they become in handwriting?

EDIT: Also important: What happens when all diacritics are left out, is this writing system still readable and understandable, or does it fail under such circumstances?


What would be the most accurate character to use to transliterate the 'e' sound in 'bet' to the Arabic alphabet?

I don't know any language written using the Arabic script, but as far as I can tell the most common approach across languages for representing /e/ is using some variant of ي.
Somali uses ئ, Pashto and Uyghur use ې, and Kurdish, as you mentioned, uses ێ. The Jawi script used to write Malay even uses ي for both /i/, /e/ and /ɛ/. Urdu uses two different symbols, ے (which is based on ي) and ہ (which isn't).
I can't really speak in terms of how recognizable any of this would be to Arabic-speakers of course, but since multiple languages that needed an /e/-like letter reached for ي, it seems reasonable to suggest that approach.
But things are never simple - ە is also quite common. For example, you mentioned Kurdish which uses it to represent /ɛ/ (which is not /e/, but pretty similar), and Persian also uses it for /e/. And as I said earlier, Urdu does use ہ (based on ه), though I believe ے is more common (except word-intially, where it can't appear).
It seems to me like some twist on ي is the most common across languages, but which one to pick is not obvious (though I expect they'd all be about equally clear to someone who isn't already familiar with one of them). ە is more uniform, but might be a bit less common, and in languages that use both (like Uyghur and Kurdish) it seems that the ي variant usually represents /e/, while ە is something like /ɛ/.
So, I'd probably suggest ێ, but either option seems reasonable.
Source: Arabic script § Additional letters used in other languages (Wikipedia) (and various language and script articles mostly linked to from there)


I'm creating a constructed language. Does this type of conlang exist?

Probably something similar already exists. Languages of this type are called somewhat despectively Euroclones in the conlang community and the field of such languages is pretty well trotted out, though most designers prefer English-Spanish blends with simpler phonology over English-French blends. Euroclones are often marketed as International Auxiliary Languages by their respective proponents.

For the personal pronouns, Ido looks like a good match.


Are there any successful conlangs using information density as a design goal?

Answering this question is tricky. As you obtain higher and higher levels of information density, you have to sacrifice some naturalism or some simplicity in order to get there.
Marking the point where you've sacrificed too much naturalism or simplicity to be learnable is a judgment call.
Short answer:
Possibly guaspi, but it's obscure.

One famous example of this is Ithkuil. Parts of Ithkuil are reasonably naturalistic, such as its phonology, which is less complex than Ubykh or Chechen (which also has a large number of vowels). Other parts are not, such as the very fine-grained case distinctions or how meanings are organized into roots, which is more complex than the system of triliteral roots in Semitic languages that it is based on.
Is Ithkuil learnable? I really don't know. My guess is no but I don't have proof.

An example of an informationally-dense written language is Classical Chinese. Classical Chinese is not a conlang, but it was written centuries after it stopped being spoken and uses a heavily abbreviated style where nearly everything that's pragmatically inferable is dropped.
If you want to make an informationally dense conlang, Classical Chinese is a good starting point. It has pervasive zero marking (although you can optionally mark possessors and relative clauses with an overt marker) and the reconstructed roots are monosyllabic or sesquisyllabic.

One possible example of an intentionally information dense language is guaspi, a tonal derivative of lojban.
I don't know whether lojban is considered learnable or not and I don't know whether to consider guaspi successful or not, but efficiency is one of its stated goals.

Gua\spi is efficient. Words are short, and extensive defaults on
articles and modal cases eliminate the majority of structure words.

In my personal opinion, so take it with a grain of salt, a human can speak "informal" lojban riddled with logic errors and this should count as speaking lojban.

Closing remarks:
Looking at some of these examples reveals an important design decision that creators of an informationally-dense language face: whether to allow the speaker to drop things that are pragmatically inferable and how to account for that when evaluating how well their language achieves its goals.
For instance, suppose a language has very specific tenses that are marked on all verbs or person marking on all verbs. Tense information is frequently recoverable from context, as are pronominal arguments. If information is recoverable from context, does the language get any points for encoding it directly, however efficiently it may do so?


Is there any easy way to find out how multiple unrelated languages express the same concept?

Unfortunately not.

There are a few concepts (like colour terms or kinship terms) that are regularly studied in linguistic typology and where one can find a lot of publications including high-level overviews including a lot of unrelated languages.

For the most concepts, there is nothing comparable available. Maybe one can find studies (e.g., from translatology) comparing a certain concept in a pair of languages or a small group of languages, but those languages tend to be the well-known big ones (English, French, German, Italian, Spanish, Russian, Chinese, and Japanese).


How would one describe different tones on paper?

I think vowel + shift in tone is key. If you'd just have different tones (as in notes) for vowels, that would conflict with expressions of pain, surprise, etc. In Asian Philology, when we talk about "tones", we actually mean a change in pitch for a vowel. Chinese has 4: Same, Up, Down and Down+Up. Thai for example has more.

Here's a grid of the most used tonal notation systems for Chinese:

The most common in use today is Pinyin


How to distinguish [i] from [iː] in Cyrillic

If ы is otherwise unused, it seems like the best fit here to me. It certainly seems at least as close a match as some others you've accepted (e.g. ц for dʒ)


The answer is a definite Yes, there are.

The example that comes immediately to my mind is Bliss symbolics (also known as Semantography) by Charles Bliss from 1942–1949. As an additional bonus, it is still used and developped further, and may even be included into Unicode at some date.

EDIT: The term to look for is pasigraphy. There were lots of pasigraphies (Blanke, Internationale Plansprachen, gives the number 60) mainly in the 19th century, but the most successful ones were created in the 20th century. There were both philosophical pasigraphies (often using digits or abstract symbols) and naturalistic ones (starting from pictograms).


How can I explain the origin of the dual number in my Slavic-influenced East Nordic conlang?

Both Proto-Germanic and Proto-Slavic had the dual grammatical number. So you could just say that your conlang retained it the whole time. Alternatively you could say that it lost it and then subsequently borrowed it again from one of the Slavic languages which retained it.

If you were after a specific source, Old Church Slavonic could be ideal because it could have a wider influence than other Slavic languages through its religious prestige status. If the religious traditions of the Slavonic Orthodox churches were very highly valued by your conlang's speakers then that would help to explain why the dual number was retained by them even though the other languages of the region had lost it.


Which features make a language easier to learn?

Difficult question. I think regularity would speed up learning, as children during language learning overgeneralise (see experiments with English past tense endings). Thus instead of learning the correct exceptions at a later stage the corresponding feature would have been learned earlier.

There is a programme for teaching Esperanto as a first foreign language, as it can be used to increase second language awareness and is supposed to make learning a natural foreign language easier. You don't have to worry about exceptions, for one thing, so you can teach the concept without having to hedge your explanations by listing all the cases where it's different.

My personal view on 'difficulty' of different languages is that all languages are about equally difficult. Some languages are easier/simpler regarding some features (English inflectional morphology), but make up for that in others (vast number of near-synonyms with different distributional characteristics in English). Toki Pona is a very simple language (120 words, virtually no syntactic complexity), so you can learn it almost in a day, but it is very hard to express complicated narratives, and an equivalent text in a more complex language would be far more concise.

Learning Esperanto is reasonably easy, but then you look at how people actually use it in everyday interactions, and you find that it is more difficult than you imagined: there are a lot of the smaller particles that make it tricky to understand for a beginner. But the 'early' sentences composed when the language was still fairly new are a lot simpler. However, they were not suitable for encoding all the pragmatic and other information people need for an everyday language.

So, there are undoubtedly features that make it easier for children to learn a language as L1, but the question is "what for?" It's a bit like learning Lisp programming: understanding the syntax takes literally ten minutes, but that does not mean you can write useful programs in it after that. Languages are more than the sum of syntax and vocabulary, and if there was a language that was easier to learn and use than other languages, and had equal expressive power, then we would all be speaking it already.


How to translate the word "lost"/"loss" into Klingon?

I would translate it as I am looking for bears and I am looking for the sheep that are lost. — I don't know the word for sheep, so I assume from your question that it's DI'raq:

  mIl'oDmey vInejtaH                 'ej DI'raqmey  chIlpu'bogh       vInejtaH
  bear-<pl> <I-them>-look for-<cont> and sheep-<pl> lose-<perf>-<rel> <I-them>-look for-<cont>

See: Klingon Dictionary 6.2 (Complex Sentences) and 6.2.3 (Relative Clauses)

Your second sentence, I can bear the loss of sheep. — I would opt for a subordinate clause, If I lose sheep, I can bear it.:

  DI'raqmey  vIchIlpu'chugh          vISIQlaH
  sheep-<pl> <I-them>-lose-<perf>-if <I-it>-bear/endure-<ability>

See: Klingon Dictionary 6.2.2 (Subordinate Clauses)

Disclaimer: I'm not a Klingon expert, so this might not be 100% accurate.