Is there a structured toki pona dictionary/thesaurus?

Proving a negative is always difficult, but as far as I can tell there is no obvious candidate for what you're looking for and if you made one yourself it would presumably fill an empty niche in the Toki Pona universe. At least I haven't found any sites written in English yet that seem to fit the bill.

The closest thing I can find to what you are looking for is a Toki Pona corpus search tool, which seems like it would be useful for tracking down examples of usage and might help you find compounds containing a particular word that have already been coined.

Also, I have yet to find two simpler things that would be good stepping stones for a hierarchically organized Toki Pona dictionary.

A non-minimal dictionary
Toki Pona-English parallel texts

All of the Toki Pona dictionaries I have found so far define just the basic vocabulary and do not provide entries for any multi-morpheme lexemes, even famous ones like jan utala.

Many of the dictionaries out there are more or less copies of the official dictionary, such as this one. Other dictionaries like this Wiktionary appendix do not provide definitions for whole Toki Pona expressions at a time.

Toki Pona-English parallel texts would help distinguish lexeme boundaries within complex phrases, since the presence or absence of pi is not a completely reliable cue as to whether a "real lexeme boundary" was intended.


Language with contextual-free vocabulary

Firstly, I have thought about this too before. Actually, only one word is needed for all of I, you, this, there, tomorrow, etc. You can analyse these as I, (the person I am referring to), (the thing I am referring to at/by/on ME), (the place I am referring to not at/by/on ME), (the day which is one day later than the day I am in). This goes for most words like those.

Not that I know of. But let's create one for demonstration purposes: Loj-ban mi. It is Lojban, but there's a ban on the word mi (and vi, and ti, and other words incorporating mi as said above).

It would be able to express concepts like 'Bananas grow on trees', as this doesn't depend on the concept I. However, saying stuff like My name is Santa Claus., It's going well. and What are we doing tomorrow? would be impossible.
We could replace it with other concepts, for example, 'the speaker/writer'. But this is ambiguous, take this sentence: I don't know who said that, but the speaker is in big trouble when I find out!. (And, pulling it off correctly, it nevertheless depends on context). Names can be used, so the answer is actually yes. 'Tomorrow' would have to be expressed as a date, 'this' would have to be 'The plate on the table in the house of Joe Example, etc.

Yes, as we proved above with Loj-ban mi, it is possible. Would it be learnable? Probably. But not usable in practice.


What are the common features of "Elvish" conlangs?

One way to look at "elvish" features is to compare how different elvish languages look, and to take inspiration from that.

A look at the phonologies of a few elvish languages:

Quenya
(phonology from here)

         Labial Alveolar Palatal Velar Glottal
Nasal        m       n              ŋ
Stop       p b     t d            k g
Fricative  f v     s     (ç)      x     h
Trill                r
Semivowel (ʍ) w             j
Liquid               l

      Front Central Back
Close  i(ː)         u(ː)
C-Mid  eː           o:
O-Mid  ɛ            ɔ
Open         a(ː)

Sindarin
(phonology from here)

         Labial  Dental Alveolar Lateral Palatal Velar Uvular Glottal
Nasal        m       n                              ŋ
Stop       p b     t d                            k g
Fricative  f v     θ ð   s       ɬ                      χ      h
Trill               r
Approximant                          l       j    ʍ w

        Front Central Back
Close   i y             u
Near-C  ɪ               ʊ
O-Mid   ɛ               ɔ
Open          a

Some common denominators in Tolkien's Elvish: They all have distinction between voiced and unvoiced stops and (labial) fricatives, both have the somewhat /ʍ/ as a phoneme or allophone as well as /ŋ/, /x~χ/ and /h/. With vowels, they each have four vowel heights but nothing much in common beyond that. Allowed syllables seem to be (CC)V(CC) in Quenya (many more details at Wikipedia) and (C)V(C) in Sindarin, though I don't see that explicitly.

Pathfinder Elf Names
(names from here)

  Male Names: Caladrel, Heldalel, Lanliss, Meirdrarel, Seldlon, Talathel, Variel, Zordlon.

  Female Names: Amrunelara, Dardlara, Faunra, Jathal, Merisiel, Oparal, Soumral, Tessara, Yalandlara.

My interpretation of the names hints at some of these features: Only two nasals, voicing distinction, five vowels.

Allowed syllables: Apparently (C)V(CC) or (C)V(LC) where L is a liquid (l or r) or nasal

Dungeons & Dragons Elf Names
(names from 3.5 edition Player's Handbook p. 16)

  Male Names: Aramil, Aust, Enialis, Heian, Himo, Ivellios, Laucian, Quarion, Soveliss, Thamior, Tharivol

  Female Names: Anastrianna, Antinua, Drusilia, Felosial, Ielenia, Lia, Mialee, Qilathe, Silaqui, Vadanja, Valanthe, Xanaphia

  Family Names: Amastacia, Amakiir, Galanodel, Holimion, Liadon, Meliamne, Naïlo, Siannodel, Ilphukiir, Xiloscient

Here we seem to have gemination at the end of words, vowel length, maybe uvular stop; th and ph are probably fricatives and not aspirated, judging by the presence of v and absence of f. Syllables seem to be (C)V(CC).

Using the very questionable methodology of taking the least common denominators of all of them would give us something like:

          Labial   Dental Alveolar Palatal Velar Glottal
Nasal        m       n
Stop       p b     t d                      k g
Fricative  f v     θ       s z                    h
Trill                        r
Approximant                  l       j       w

        Front Central Back
Close   i               u
Mid     e               o
Open          a

If you want an elvish language to be easily recognizable as elvish, you might be able to copy some of these features. I'm not sure, though, that there is any feature that might be universally understood as elf-like.


Constructed languages or dialects for Time travellers

Ted Chang wrote "Story of Your Life" which was the basis for the movie Arrival. I thought both the book and the visual representation in the film were excellent examples of languages based on a travelers use of time. In this story understanding the language is to understand your life as a simultaneous event, and thus have access to all moments at once.

You may also want to consider Jargon specific to your vision of time travel. Do paradox occur, and if so what is the resultant outcome? Do parallel realities exist, are there different types? Can futures be erased or overwritten, if so, what do you call a future that no longer exists, or a person lost in one? Do you have some sort of McGuffin for the travelling part? Is the language the means of travel? Do bodies travel or only minds?

You might consider leveraging something like Hobo signs, notes left by other travelers, with help or warnings, that type of thing. Alternatively, Signals of fealty and place, such as a question and response or sing the local anthem to identify other travelers as friend or foe. Flushing out what you want them to communicate, as well as the mood or archetypes of the speakers, might help drive the sound and appearance of the language.


How many words should I create in a conlang?

The answer to both of these questions lies somewhere between "it depends" and "let's speculate a little".

The act of inventing a naturalistic language does not necessarily mean that you must also create a naturalistically large lexicon. After all, it's the grammar, the syntax, the usability in a wide variety of normal contexts that determines naturalism.  A natural language might have anywhere between 15000 and 1,000,000 words. And as you can see from the several English entries, there's not even a consensus as to how many words there are in a language. The number of words you should create is entirely up to you. A more interesting question, interesting in the broad sense of course!, is how many words is enough words to create? This is not only more interesting to consider, but also harder to answer because there is no pat response and any answer given will be purely opinion.
I'd argue that 2000 is a bare bones lower estimation, given that this is the lexicon size for Basic English. But B.E. isn't exactly "naturalistic", so that figure is undoubtedly low. Somewhere between 3000 and 6000 gives you a little more than dry bones to gnaw on!, but still hardly approaches the naturalism of a natural language, to say nothing of the works of the more gung ho kind of lexicophilic glossopoets!

As for the second question, we do have some recent figures. The results of a recent survey of language inventors determined a spread of approximately 500 (+/-) to >5,000 over 246 respondents. Of note are the lowest and highest categories, with about 70% of respondents falling into the <500 & >5000 categories. The remaining 30% fall between 500 and 5000 words.


Are there any small scale auxlangs that are actually used by a substantial amount of people?

The line between "conlang" and "supradialectal standard" can get incredibly fuzzy. You mention Rumantsch Grischun and Modern Hebrew yourself, something along similar lines, but much more successful in terms of number of speakers is Bahasa Indonesia. Any number of other supradialectal standards depending on how strict you are with drawing the line may fall under this category.

In addition to supradialectal standards, another thing that may or may not be considered a conlang is controlled languages, such as ASD STE-100 Simplified Technical English which see some use in various technical documents (but aren't really spoken).


Logical Language Group, Inc. retains the copyright, but grants permission to copy, redistribute, and create derivative works from the official book, under conditions such as attribution and a requirement to include a permission notice identical to the one below.

Copyright © 1997 by The Logical Language Group, Inc. All Rights Reserved.
Permission is granted to make and distribute verbatim copies of this book, either in electronic or in printed form, provided the copyright notice and this permission notice are preserved on all copies.
Permission is granted to copy and distribute modified versions of this book, provided that the modifications are clearly marked as such, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one.
Permission is granted to copy and distribute translations of this book into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation that has been approved by the Logical Language Group, rather than in English.
The contents of Chapter 21 are in the public domain.

From the Boring Legalities section of the Lojban Reference Grammar
The Formal Grammar (chapter 21) is in the public domain, as the above license says.


The best parallel for Turing completeness in human languages is the Natural Semantic Metalanguage. The NSM proposes that there is a limited set of basic semantic concepts which all human languages have, and which are not reducible to other concepts. They call these "semantic primes", because you combine them to get all other meanings, and because they can't be broken down. The list of primes, currently numbering 65, is a work in progress as new primes are proposed and evaluated, but after over 45 years of work on the theory the list has proven to be very reliable and new primes are only rarely proposed.

The NSM is a good guide therefore for judging whether a conlang is "complete" - whether it would be as capable for expressing human thought as any natural language. If a conlang has vocabulary items (they can be words, affixes, or phrases) for each of the semantic primes then I would judge it to be complete.


What's the purpose of vowels and consonants?

This is somewhat similar to "what's the purpose of odd and even numbers".

Looking at the sounds produced in human languages we can distinguish two different ways of articulation, one where sound waves are produced by the glottis, modulated in the vocal tract through opening of the jaw (open/closed) and position of the tongue (front/back), but otherwise pass through unrestricted.

The other type of sound does not depend on the glottis (whose action is optional), and an airflow is generated coming from the lungs, passing through the vocal tract; but this time, there are constrictions at various places of articulation, which modulate the frequency spectrum of the resulting sounds to produce significant differences. Depending on whether the glottis is active, these sounds can be classified as voiced or unvoiced.

The former are called vowels: they are always voiced, and are defined through the positions of jaw and tongue. The latter are consonants, and are defined through the place of the constriction (glottal, dental, labial, ...), the nature
of the constriction (fricatives, stops) and whether they are voiced or unvoiced.

As it happens, you kind of need both kinds of sounds in a language to make it pronounceable. Just like you need odd and even numbers to do maths.

You can see this in syllables: a syllable has to have a vowel as its central element, and is surrounded by consonants. You can have different syllable structures: CV, VC, CVC, etc., and depending on language some structures are more common than others. But this is more of an emergent feature than some deliberate decision.


Language with nominal TAM and no verbs: Ergative or tripartite?

In your example:

  Then, the actual translation for "the woman sees the man" would be
  "the womans sight the man". And that's the problem: "sight" and "man"
  are both unmarked nouns, leading to misinterpretation.

...sight is a verb.

In order to have a verbless phrase, you'd want something like "the man within the woman's sight", making it clear you're using the noun "sight" and not the verb "sight".

However, and I've seen this pointed out, if you end up needing particular constructions in order to indicate actions, all you're doing is making an overly complicated verb.


What are the benefits of inventing irregular verbs in one’s conlang?

Irregular verbs are naturalistic.

For this reason, even an international auxiliary language, namely IALA Interlingua, has irregular verbs to match its Romance source languages (that are famous for their wealth of irregular verbs mostly directly inherited from Latin)

Irregularities add flavour to your conlang.

They make the conlang as a whole more interesting and create some esthetic effect. It also shows that the conlang designer has spent some more time to make Eir creation not too schematic.


How would you say "good morning" or "hello" politely in Klingon?

This answer is based largely on my copy of The Klingon Dictionary (written by Marc Okrand, who created Klingon), which is reliable and good if you need a quick translation from English to Klingon or vice-versa. I'm going to cover most of the same ground as rotaredom's answer, just in more detail.
The book notes that there aren't really any greetings in Klingon; they're simply unnecessary. Klingon as a language is somewhat utilitarian in its application, and exchanges typically start with a straightforward statement or query by one party. Saying the Klingon equivalent of "How are you doing?" when you just want to figure out the new ship's departure time is simply wasteful. One answer to your question, then, would be to simply avoid a greeting. The less you talk, the less time you take up. That said, if you want to truly greet someone, you have two options. . .
Choice 1: Be utilitarian.
This utilitarianism is why all Klingon "greetings" are just introductory phrases. "nuqneH" is the one that seems to be commonly used, as rotaredom said. Its translation is "What do you want?" "Nuq" itself can be treated as an interrogative sentence on its own, simply meaning "What?"1. It can also be used as the start of a sentence, such as

nuq legh yaS

which means

What does the officer see?

Additionally, "neH" is used as a form of "to want" (though it also used as an adverbial, to mean "only"). Therefore, we have the compound "nuqneH", properly an exclamation that stands by itself as a sentence.
Choice 2: Use an honorific.
The Dictionary notes that "neS" is the only honorific suffix in Klingon, used as part of larger words. For instance, "qaleghneS", coming from "qa" ("you"), "legh" ("see") and "neS", translates to

I am honored to see you.

This states a fact, and gets to the point. It may be used towards a superior, but this is not mandatory, and I don't think it's commonly used. If you wish to open the conversation with an inquiry, "HIja'neS" (which includes "HIja", normally used as an affirmative) can work. Its translation is

Do me the honor of telling me [about something].

Again, use this when asking a superior something, but only if you really want to be respectful.
Miscellaneous
Though I have yet to see any of the following used as a greeting, I imagine you could modify them to create some sort of opening remark.

"bel" is the verb for "to be pleased", so when greeting someone, you could conceivably say "jIbel" ("I am pleased", with "jI" for first-person). Likewise, "Quch" is the verb for "to be happy". Using "jIbel" or "jiQuch" to indicate satisfaction upon meeting someone is a possibility.
"maj" ("Good") or "majQa'" ("Well done") are exclamations used as praise. You could use these - preferably "majQa'" - when welcoming an inferior who has successfully completed a task, like blowing up an enemy spaceship.
"toH" is another exclamation, meaning "Well!" or "So!" You would use this in, for instance, a sentence like

Well! I didn't expect to see you back alive.

1 Appending "Daq", to make "nuqDaq", yields "Where?"


Is there any evidence that learning a zonal Slavic conlang can help conversing with native speakers of Slavic languages

Yes, they show. Slovio is not a zonal conlang, it is supposed to be a kind of Slavic Esperanto. It took place 20 years ago, but nowadays noone wants to use it.

Nevertheless, Interslavic is comprehensible for all Slavic people. Speaker of Interslavic went abroad to different Slavic countries and expressed their idea using Interslavic instead of native languages or English. And it worked. People understand the meaning, though the language can sound strange or event funny to them. And if it does, Interslavic is a viable project and succeeds in its challenge.


Syntactic word that carries no meaning - is there a name for that?

One general term would be function words; these are words that do not carry any lexical meaning, but are used to link content words together and clarify their relationships (eg in the case of prepositions or conjunctions).

It is indeed difficult to see exactly what you have in mind without any examples; other possibilities would be particle, which is eg used in Japanese to mark certain grammatical features (such as 'direct object').

Some people use the term empty verb for the auxiliary in phrases like to have/take a shower, where you could just use to shower directly; here you can add the tense feature to the auxiliary as in She had/took a shower.

As an aside: there are no words that "carry no meaning". If a word has no meaning, it is redundant, and would not be there at all. In linguistics you distinguish between lexical meaning and functional/grammatical meaning: the former you would find in a dictionary definition, whereas the latter is not always easy to put into words, as it describes relationships between elements in and structure of a sentence.

Update after example: Hard to say. A particle usually doesn't change its form (at least in English and most other natural languages I know), so the fact that the marker -to is attached to it would rule that possibility out in my view. That would leave empty verb as the most likely option, but then it is not really necessary when the marker is not used. I guess it would still be my preference, though.


How does Láadan aim to express the views of women more than natural Western languages?

I am not an expert on Láadan but I was also researching it in the context of feminist communication.  This is what I found based on that research.

The idea behind creating Láadan as a "feminist" language was to test the Sapir-Whorf Hypothesis to see if natural languages were biased toward expressing male communication, but the language's creator, Suzette Haden Elgin, was unable to prove or disprove the hypotheses she set out to study because of low adoption of the language.  As far as I can tell, even Elgin remains uncertain on the effect of these approaches to facilitating feminine communication.

The distinctive characteristics that strike me are

It is a tonal language - This seems to have been very deliberate in the development of Láadan. Does this facilitate feminine thought with particularly more clarity than non-tonal languages?  I am not sure, and I couldn't find any reputable research indicating whether or not that is the case, but I suspect that when the language was being developed by Elgin she did not make it a tonal language by accident.  Since her hypotheses about the implications of Láadan on the Sapir-Whorf Hypothesis remain unconfirmed, we probably don't know for sure.
The language has emotional context markers.  This is presumably meant to aid in the expression of subtle emotional context to avoid ambiguity that leaves a dialogue open to interpretation and reliant on context clues.

-d anger marker
-th pain marker
-li love marker
-lan celebration marker
-da joke marker
-di education marker
-ya fear marker

The language has many affection words, for example, of love.  Like the other aspects, whether this is truly a facet that favors female communication over male based on empirical evidence is unclear to me, but it certainly satisfies many widely accepted assumptions about differences in male and female thought.  However, it should be noted that many of these assumptions are widely challenged today.  Perhaps men desire more nuanced emotional communication as well but suppress this impulse for cultural reasons.

a love for inanimates
áayáa mysterious love, not yet known to be welcome or unwelcome
áazh love for someone sexually desired in the past, but not anymore
ab love for one liked but not respected
ad love for one respected but not liked
éme love for one neither liked nor respected
am love for one related by blood
ashon love for one not related by blood, but kin of the heart
aye love that is unwelcome and a burden
azh love for one sexually desired now
oham love for that which is holy
sham love for the child of one’s body

These text examples were taken from this online PDF resource.


What's a good starting place to work on vocab?

If you're new to conlanging and want to start an entire language from scratch:  I would recommend reading The Language Construction Kit by Mark Rosenfelder.  It's a fun read and is very helpful to a new conlanger, and helps you know what to create for your purposes, how to do this, and gives you a good understanding of basic linguistics.

For creating vocabularies from scratch:  A common practice is to begin with a list of roots and expand outwards, usually using some kind of derivational morphology.  The words you're going to want to begin with, besides words that come up in your grammar, which I think should be close to done by the time you start building a lexicon, are the basic concepts.  Things like man, tree, water, eat, do, green.  One famous example of such a list is the Swadesh list.  The way I made my vocab for my first language, Simean, was by coming up with roots for the concepts on this list and using morphological rules to expand that list.

Another alternative, though one I don't personally use, is to simply translate things and make up the necessary words as you go along.  Even so, I'd start with the Swadesh list to get a good grounding in terms of what your language feels, looks, and sounds like.


What are common origins of accusative case markers?

This is merely a marginal answer and I’m sure there’s a lot more data that might prove valuable, but in multiple Romance languages (at least Spanish and Romansh) the preposition a has developed into an accusative marker for particularly animate objects. This preposition derives from Latin ad “to(wards)” and is in both languages somewhat equivalent to English to or at in usage (in Romansh it is commonly used to mark the dative as well, as in French).

In general I would not be surprised to see allative or dative adpositions turn into accusative markers, there is quite a bit of overlap in the meanings (compare “I hit towards you” and “I hit you”).


Was Tolkien aware of the Voynich manuscript?

Or, to the opposite, was Tengwar already designed before the Voynich manuscript was rediscovered and publically known?

The manuscript was rediscovered in 1912. Tolkien, according to Wikipedia, started developing Elvish in 1910 or 1911... before the Voynich manuscript was rediscovered.

There is at least one claim that he was aware of it, though, although it would have to be after he had already started developing the languages.

This is a transcript of a message sent to the Voynich mailing list, sent November 13, 2002:

  Hello
  I have "lurked" on this list for a while and finally have a comment to offer, albeit a very insignificant one.

  I wonder if the fact that Prof. JRR Tolkien apparently had an interest in (or at least knowledge of) the Voynich Ms has been discussed or indeed is of any interest at all?

  The thing is, a nagging feeling that I had once seen the VMs many years ago - long before my recent interest was sparked by that piece in The New Scientist - is resolved. I now recall it - and though the persons concerned having died long since makes my little anecdote mere hearsay and in no way veridical, I thought I'd forward it. An old friend, a retired military man with an amateur interest in codes and cyphers, once showed me a couple of not entirely distinct b&w copies of pages from a curious coded manuscript, which I now realise were a couple of folios of the VMs. I was not especially interested in them at the time, I think, but the reason that the incident made an impression was that he said that they had been given to him by Prof JRR Tolkien. At that time I had just discovered and was very much 'into' Tolkien so I was most envious of my friend's knowing him and pressed for details of the great man, though in the end I never achieved my longed-for personal introduction. So I now wonder if there might be any reference anywhere in the mass of Tolkien papers to our VMs, and is this of any possible slight significance? After all, JRRT knew a great deal about languages and artificial scripts of course and if he was interested enough to make and pass on copies to a friend, he might have devoted some time to the VMs himself. And the Voynichese script does have a Tolkien-ish look to it or vice versa: could it have influenced him?

(this was found through a link from CipherMysteries.com)

However, since his development started before the Voynich manuscript was discovered, I'd say that it's... kinda unlikely that he was inspired by it.


Alternate direction systems for spatial reference

Okay. How about instead of an egocentric direction system, employing a listener-centric or "you"-centric system? We do this in natural language when we say "On your left" or "At your 3:00". Probably such a system would be developed among speakers from a highly empathetic and listener-oriented culture, where the individual's reference is considered secondary to the listener's.


After a research, I finally found this example which explains this.

  si quieres decir una perra (adulta) pequeña, el orden adecuado es entonces perra+pequeña = hundineto. El orden contrario es poco natural y hace dudar al que oye la palabra hundetino = perrito hembra

So the valid ones for Little princess are:
1. Mikra princino = "Little" + "female descendant of some royal crown"
2. Princineto = A female descendant of some royal crown who is little.

"Princetino" would be like:
A little descendant of some royal crown who is female.


How does mood relate to tense and aspect?

(For tense and aspect in general, see this answer)

I'll summarize what Mark Rosenfelder says in Advanced Language Construction, pp. 146-156 (some of which referring back to Mood and Modality, F.R.Palmer 2001).

First we start with modality, which is concerned with the status of the proposition, i.e. "how true it is, and whether it's subject to obligations and intentions". In contrast tense (at its most basic degree, ignoring semantic expansion) is interested to whether it happens before or after now, and aspect with overall temporal relation (hence the possibility of contrast between tenses within a given aspect).

Rosenfelder describes Palmer's classification of modals like so:

Factual

Epistemic: speculative, assumptive & deductive
Evidential: reported, sensory & deductive

Deontic

External: obligative, permissive, commissive
Internal: abilitive & volitive

(Most discussions bundle all of the "factual" branch as one "evidentials" category because languages with evidentials tend to have only one of the two sub-branches, which is also why deductive is listed twice without being self-contradictory)

Basically working from that, a mood is what happen when modality bundles up with tense, and there it gets a little messy. Terminologically, Rosenfelder believes that indicative/subjunctive and realis/irrealis systems are separated more clearly by geography (specialists in given language families prefer one or the other) than grammatical reality.

In any case, realis/indicative applies protoypically to real events, irrealis/subjunctive to "less real" stuff. What is included in each category may vary considerably (future events and imperative may categorize in either one, for example, depending on individual languages). Conditionals are irrealis in virtually all systems, but in Indo-European linguistics are traditionally treated as a third mood separate from both indicative and subjunctive.

In practice, moods are often more of a semantic division within the verbal paradigm owing to the lack of a separate marker for them (in most European languages I'm aware of, for example). When an explicit irrealis marker exists, it often takes over separate marking for tense and aspect, that is, there will be no overt marking of the subcategories like future vs. imperative (both only irrealis) or past vs. present (both realis). Manam is such a language (how unusual this is is unclear from Rosenfelder's writing).


Note that you as the conlang designer control both ends of the chain: The final wordform and the etymology. So you can play with both parts until the result meets your wishes.

So you can start with the wordform Amrar and search for an etymology, splitting it up as Am-rar and find some meanings for Am and rar, say am is short for amon "hill, mountain" and rar is "roar, load noise", making your mighty dragon a "moutain-roar(er)". Tolkien used this approach a lot. The backside of this approach is that the conlang becomes difficult to maintain.

EDIT: Going the other way, starting with arán and kile, you can vary the order of the two stems, Maybe Kilarán sounds better than Aránkil?  It is your decision. You can also throw in some sounds between the two stems, say Aránskil with an inserted s, you can insert a vowel, say a, to yield Aranakil, you can assimilate the n to the k giving Arángkil.

Starting with roots from your conlang, there are still a lot of creative possibilites to combine them in compounds: Inserting a Fugenelement (example from German Herz-ens-sache "affair of the heart", from Herz "heart" and Sache "thing, affair", ens being the Fugenelement without meaning), applying some assimilations or dissimilations, dropping syllables from long words (syncope), ...).


What is the key to realistic inventories

You should think of phonology  in terms of distinction. You have to distinguish certain consonants and vowels from others, and you have to figure out the best way to do that.

A realistic inventory has spread out places of articulation, often symmetrical. It's much easier to make a distinction between spread-out consonants that between consonants that are articulated similarly. That's why this is a really common inventory:

             Front Central Back
Close        i             u
Near-Close
Mid-Close
Mid          e             o
Mid-Open
Near-Open
Mid-Open           a

And this is unheard of:

             Front Central Back
Close        i             u
Near-Close   ɪ             ʊ
Mid-Close          ɘ
Mid
Mid-Open
Near-Open
Mid-Open

You should always make sure a language makes distinctions that are spread apart, e.g. /p t k/, rather than distinguishing three types of t-sounds /t̼ t ʈ/ without also having a distinction from /p k/ (unless for some reason you're making a language to be spoken by aliens without lips, for instance). There's also no reason to have only three consonants /p d kʰ/; you should either have only one set (such as /p t k/), or have a set for each of them (i.e. /p pʰ b, t tʰ d, k kʰ g/).

Every rule has its exceptions, but this is true of most natural languages, and you should use this as a starting point.

(Some more details can be found in my answer on Linguistics, from which I copied some of the examples)


Is is okay that most consonant assimilations result in a phone whose dedicated letter doesn't exist?

I would argue that the orthography of your conlang is not just OK but really excellent given your description of the phonology.
Why is this the case? It keeps the number of letters needed to write the language in a very comfortable range. The additional sounds are given by digraphs, a method that is often preferable over adding more letters to the basic alphabet or adding diacritics to the base letters.
I also imagine that the orthography keeps morphemes recognisable assuming that at least some morphemes are just CVC syllables and combining them results in assimilation.


What setting for the dropoff rate in a language generator will produce a natural English phoneme distribution?

Note that by synthesising vocabulary using a tool like Vulgar Lang, you will not even approximate English even when using the same distributional laws for phonemes. You will get a lot of words that could be English, but are just unused, you get known words but with other meanings, and you don't get morphology or syntax at all.

Of course, "naturalistic ranking" is the best approximation, all other rankings lead to feelable statistical distortions given your conlang an engeneered touch.

As an alternative I suggest looking at the questions and answers under diachronics: Start with real life English and apply systematic changes to the sounds and the grammar. For an example using projection of current trends into the future, you can look at Futurese.


How many different interjections like 'aha,' 'oh' would you make up for a conlang?

This is as much a question of invented culture as it is invented language. Strictly speaking, one can devise as few or as many such interjections as one likes. Likewise, the breadth and depth of meanings, overlaps and distinctions are similarly up to the inventor.
I'd argue that if the speakers of the invented language sense the need to distinguish "aha" from "oh", then the discoverer of their language ought to take note! Likewise, if they divide the semantic space of "aha" into three distinct areas, or if they don't distinguish "aha" from "oh", then that should also be noted.
As for the question of which are worth making words for: that's more a matter of pragmatism. Most language inventors engage with the art out of inner joy and as an expression of fundamental creativity and generativity. Making words is almost never a problem for most language inventors! If she should discover that the speakers of the invented language have a little used interjection, a word will surely present itself!


How to develop a detailed, realistic a posteriori conlang?

So, you are going to create an altlang (a naturalistic language living in an alternate history of the the world). First, define your starting point (easiest for the first scenario: Old Irish or proto-Goidelic is a suitable starting point for this one). Look at the real world descendants from that starting points (Middle Irish and Modern Irish, Manx, Scottish Gaelish) and what changes happened to them. You can create variation by retaining some archaic features, applying changes from different descendants, or applying changes in different temporal order to create a new artificial Goidelic language. You may also throw in some original changes not occurring in the known Goidelic languages. Keep a timeline of those changes—the changes will apply to loan words as well!

Than decide on the influence of the other language: Are there only borrowings of words, shall it influence syntax (e.g., the order of noun and genitive or noun and adjective, shall the basic word order change?), are there new phonemes added to the phonology?

Decide, when the influence happens, does it happen only once, are there several waves of influence. Note that the other language changes over time, too. Your conlang may preserve archaic words from the donor language that have fallen out of use or have undergone sound shifts there.

Put everything together and enjoy the result!


Is there any way to figure out the phonotactics of a language and
create words that sound like they fit in, without having to learn an
insane amount of linguistics/"source language"?

There is: look it up. For example: Nahuatl Phonology.
Nahuatl phonotactics turn out to be pretty simple: maximally one onset consonant, a long vowel, and one coda consonant per syllable. Here's an Awkwords script that'll give you 100 random 3 syllable words conforming to Nahuatl phonology:
#awkwords version 1.2
V:ii/i/ee/e/uu/u/aa/a
C:m/n/p/t/k/kw/h/ts/tl/tc/s/l/c/j/w
r:(C)V(C)CV(C)CV(C)
n:100
nle

If you don't care about the source language morphology, that oughta be good enough. Not all of the words will be winners, but you can generate tons and just pick the few you like best.
To get words that really look like plausible source-language words, though, you do need to care about morphology. In that case, you do have to learn something about the source language, but not necessarily "an insane amount". For example, a simple change to that Awkwords script will generate plausible dictionary-forms of Nahuatl nouns with 3-syllable bases and <-tl> or <-tli> suffixes:
#awkwords version 1.2
V:ii/i/ee/e/uu/u/aa/a
C:m/n/p/t/k/kw/h/ts/tl/tc/s/l/c/j/w
r:(C)V(C)CV(C)CV[tl/CVtli]
n:100
nle

It is not too hard to look up lists of other morphemes and add their patterns into your word generator. If you want to get really fancy, you can try to find a pre-made computational morphological model for the source language (e.g., a PC-KIMMO or KLEENE or HFST file) and then generate random underlying forms to run through it, but that probably does start to get into the realm of "an insane amount of linguistics"...
There are a couple of decent middle ground, rather than copying the source language morphology. One is to generate a bunch of short, one-or-two-syllable con-morphemes of your own that match the source phonology, and then use those as the base units from which you generate conlang words, rather than going directly from the phonology.
Another is to try to imitate the source language phonemic distribution. For that, you basically just need a big list of source language words, from which you can extract statistical information. The simplest way to do that is to just count up occurrences of each phoneme, but if you know a little bit more statistics, or are willing to learn, you can construct a conditional distribution model for which phonemes occur most often in different particular positions, and then generate random words based on those specialized distributions, rather than the default uniform distribution. Awkwords can't handle that kind of model sophistication, but other word generators, like Logopoeist, can, and it's also not too hard to write up a custom generator just for your particular naming language.


The most prototypical evidentials are a class of verbal affixes. They are not commonly tenses or moods of their own (though they can be). As such, they are not structurally incompatible with the irrealis/conditional, and ultimately it really depends on what exactly that mood is being used for by a language.
In Quechua, counterfactuals (If I had hooves, I'd be a horse) use the irrealis marker -man, but cannot (as I understand it anyway) take evidentials, but a statement of probability (She may be at school), which also uses the same marker, definitely can.
Irrealis statements about future events or hypotheticals, on the other, can also reasonably be said to be semantically unsuitable to use evidentials: in I will try to feed her some soup, the "feed her some soup" subclause is not really a statement you can really describe the source of the information (unless you have a dedicated evidential for that case, but natural languages don't). Nonetheless, WALS notes that some languages do:

Because evidentials are used to describe the speaker’s involvement with events, they tend to occur in realis contexts, especially in past tense situations. Nevertheless, evidentials do occur in what can be described as irrealis situations. Example (9) from Barasano (Eastern Tucanoan; Colombia; Jones and Jones 1991: 116) shows an interrogative evidential, and (10), from Tsova-Tush (Nakh-Daghestanian; Georgia; Holisky and Gagua 1994: 180) shows an evidential with a future event.


What are some examples of mathematical conlangs?

There's a language based on stack-based programming languages (like Forth) that eliminates syntactic ambiguity called Fith. The name is a deliberate pun on Forth.

FrathWiki
2019 Smiley award page
Fith grammar (archived)

Basically, when parsing the language you have a stack of objects that you have to keep track of, as well as some global state like the default number that can be explicitly changed.
The idea of layering a human language on top of a Forth-like grammar is flexible enough that you could extend Fith or make radically different design decisions without losing some of its nice properties.


Whoever told you Esperanto lacks verbal aspect was lying to you. Yes, aspect isn't mentioned in the 16 Rules. However, this clearly doesn't mean Esperanto completely lacks aspect -- the 16 Rules are not intended to be a linguistically rigorous analysis of Esperanto, but merely a set of easy rules to teach laymen. Zamenhof definitely designed Esperanto containing some aspectual markers, especially given the amount of influence he took from Slavic languages; what is unclear is exactly how much aspectual information he intended to be encoded in certain markers.

Based on your description of Esperanto's complex tenses and your claim that "these aspects do not even occur in a pure form in English", you seem to be under the impression that to truly be present in a language, an aspect must be marked by a single morpheme rather than through syntactic constructions like the verb + participle constructions in English and Esperanto "complex tenses." However, that isn't how that works. The English present/past continuous constructions do mark progressive/continuous aspect. The English present/past perfect constructions do mark the perfect, though "perfect" is a bit more of a complex mix of tense and aspect than it is pure aspect. The fact that certain syntactic constructions are used here rather than a single affix does not make the aspectual marking here any less "pure".

There actually has historically been some debate over how Esperanto participles mark aspect when used in complex tenses. Zamenhof himself saw Esperanto participles as marking a mixture of tense and aspect, and this resulted in a divide among Esperantists regarding whether to translate, say "The house was built long ago" with estis konstruata (because the participle happens at the same time as the main verb) or with estis konstruita (as the building is accomplished and focused on describing its result). The latter group largely won out with an un-official notice from the Academy in 1965, which gave the following positions:

  The Esperanto tense system consists of but three tenses: the present, the past, and the future.
  All other time relationships (such as the pluperfect, future perfect, etc. of many other languages) are expressed by adverbs, conjunctions, or simply by context.
  The six participles, used either with nouns or with the verb esti, show aspect, not tense. They show, in other words, in what phase of the action the subject finds himself with respect to the object: whether beginning and unfinished (-ant, -at), finished and fulfilled (-int, -it), or not yet begun but intended or awaited (-ont, -ot).
  Accordingly the forms with -ata focus upon the duration or repetition of the act, and the forms with -ita focus upon the result of the act. The forms with -ita can also show priority in time in the event that there is separate evidence of that in the sentence, such as a word like jam = “already.”

(Quoted from Being Colloquial in Esperanto's Appendix on Participles, which goes into more detail about the conflict here.)

While this treatment of Esperanto participles are markers exclusively of aspect is technically not an official order from the Academy, it has generally been treated as such my most Esperantists, and this is largely how Esperantists use participles -- the -anta/-ata participles marking the continuous/progressive, the -inta/-ita participles marking the resultative, and the -onta/-ota participles marking the prospective. This is consistent with how they're used outside of the complex tenses as well. Based on this, one would have to willfully ignore a lot of Esperanto usage and convention to claim its participles don't mark aspect.

In addition to the obvious aspect marking on the participles, it should also be noted a few other affixes mark what could be considered aspect. You've mentioned ek- as a marker of inchoative aspect yourself (it could also be said to mark the momentane). -iĝ- could also be said to have some inchoative flavor to it (though it's a bit more obscured among its other functions, consider that eksidi and sidiĝi are near-synonymous), and -ad- similarly can mark something like continuative or iterative aspect.


Are there any Conlangs using Chinese characters?

Toki pona is a minimalist language with a ~125 word vocabulary that can be written using a proposed system of either Chinese or Japanese characters, although it is officially written in the Latin alphabet.
On tokipona.net, click on "Word List" in the group of links at the top for the full list of words, or compress for ways to write it using different alphabets. 言良り良去私 (toki pona li pona tawa mi)='I like toki pona.', literally 'toki pona is good to me'.


How could a conlang enforce subjective idealism in a constructed world

You may be interested in E-Prime.

E-Prime is a version of English that excludes all forms of the verb to be, including all conjugations, contractions and archaic forms. This makes many objective statements like "Roses are red" impossible. Instead a person is required to use more subjective constructions like "Roses appear red to me".


Are there any examples of artificial creoles of natural languages?

To name a few:

Da Mätz se Basa: High German.
Old Piscean: British English.
Kjā: Yoruba.
Cheyoon: Mandarin.
Al Mastizu: a creole of English, Spanish and Arabic.