So... this all started with a story that I made for a class called "The Chocolate Rain", and I needed some names, so I made up some names and put a bunch of diacritics on them to make them look foreign. At this point, I didn't have any intent to develop this into a full language. Then, a few stories later, I made a story involving both the country of Ḱĺk̀ and the country that I'd previously made, thus establishing that they were in the same universe, and I continued to make stories in that universe, though I wasn't always consistent with names (and the relation between Coculaght and Súiⱥcúil).
Then, later (early 2009 I think), I decided to actually start making the language, and of course I wanted to make it at least somewhat consistent with the names I'd already used... which meant assigning meaning to various diacritics that I at some point found out weren't actually in Unicode, so I decided that some of the diacritics just involved how the words changed when they changed forms. The meaning of ⱥ and ø was also decided due to how I'd made those letters pronounced on a whim way back then.
A few other things about how I decided certain things:
Thought sometime not too long before I started the language: Spanish has grammatical gender, but gender shouldn't be that important... that's like having grammatical eye color! So, when I decided to make a new language, I included grammatical eye color. I added Type 2 adjectives with the thought that at some point in the past they discriminated so much against blue-eyed people that there just wouldn't be a way to get the word for "good" to agree with blue-eyed gender, and later agreement endings were added to Type 2 adjectives copied from Type 1 adjectives.
My reasoning for making brown-eyes the default for mixed or unknown gender: male is the default gender in Spanish; maleness is sort of kind of genetically dominant (like dominant genes, it's what you get if two chromosomes are different (XY)); brown eyes are also genetically dominant.
I don't think it's a coincidence that the vowels I used for grammatical gender (e, i, u) are exactly the vowels that Spanish doesn't use for grammatical gender, though I don't remember if that was a conscious decision. The plural suffixes ub, ig, and eb are based on the first letters of the English words brown, green, and blue, respectively.
The verb endings were supposed to be fusional, but I guess I was uncreative. (Also, I didn't know at the time about fusional vs. agglutinative distinction; I just thought what Spanish did was normal...)
i almost always changes to e in the second form because i has a dot over it normally, which looks like a diacritic, and I'd decided to use diacritics to indicate stem changes.
The first– and second-person pronouns were similar to pronouns I'd used in other conlang sketches. The way third-person pronouns work was inspired by declaring variables in programming languages.
Some thoughts years later coming back to this language after I'd already started Lwaitel and Tydotsuy and gained more linguistic knowledge:
I have no idea how this particular system of vowel changes could have developed naturally... maybe I should make this be a conlang in-universe, like Lwaitel, to explain it. (In particular, the fact that vowels sort of switch places seemed perfectly okay at the time, but it seems unlikely to arise by the processes that I understand cause actual vowel changes like that in real languages... though Spanish sort of has something like that in the subjunctive).
I can make fonts now! No more approximating plusses with x's, no more misaligned diacritics!
Gaa! Stress! Specifically, I had no information whatsoever about where stress should go, but still had some idea of where stress should go... and it wasn't predictable, so I'd have to go through every single word and assign stress, but it also changes based on what suffixes are added, so... so stressful! I considered just getting rid of stress altogether...
I couldn't pronounce /r/ then, and I still can't pronounce it. I can pronounce /ɾ/ just fine, and usually /ʀ/, but not /r/.
The words for "color" and "brown" are similar (and similar to the English word "color"). Some people might see this as having something to do with outdated racist terminology; this was very much not intended, or even something I was thinking about when I made the terms. The reason they're similar is because of the color creation myth, where brown was the first non-gray color created, which is because it's both common in nature (e.g., wood, soil, many animals' fur) and doesn't fit into the rainbow, and also because of sepia photographs.
2009-08-12: first published version
2010-03-20: added many words
2010-08-30: added a bit more explanations, added phrase "puin ⱥt timce"
moved section about dates to be with the vocabulary
noted contraction er'
changed laght→laght=white (and derivatives), changed ahⱥ→pahⱥ=before, some minor corrections
2010-09-26: clarify iledⱥ and onledun
2014-11-11: made this into multiple webpages, like my newer conlangs; added a phonology chart; added a font that can display the characters in Súiⱥcuili correctly
2014-11-15: add examples that I made a long time ago; added "lo", "ol", "tu-", "ti-", "ʃu-", "ʃi-", "cu-", "pu-", "onic", "ce-", *"pilun", "Súiⱥcúili", and "r'" to the lexicon (previously they were only mentioned in the grammar); added audio for the name of the language
Ŋinun and cilun now say they are derived from Lwaitel; this is true in-universe, but out-of-universe I made the Súiⱥcúili words before I'd even decided that there would be a Lwaitel language. Making these words derived from Lwaitel was my intent when I first added the words to Lwaitel. Also I added a list of basic color terms.
#2015-11-10: +24 words (554), reanalyzed the phonology
Changed ⱥhololipsun → ⱥhololispun "camera" (original might have been a typo), scilⱥ → iscⱥ "hot" (because of phonotactics); removed dots from over i's in many function words, and changed sluril → slurıl "probably"; changed the definite form of soctun from saght to soght; made cilun "cyan" no longer a basic color term, and made color terms applied to humans refer to eye color
Changed the phonology (which didn't change many words): affricates are now phonemes, /ɚ/ is now classified as a vowel, maximal syllable is now CCVCC rather than CCCVCCCC, /r̩/ and /ɾ/ are no longer separate phonemes, /ks/ is no longer explicitly allowed as an initial cluster (it was never used in any words), some other clusters are disallowed that weren't before, /h/ vs. /x/ vs. /ɣ/ is now analyzed differently.
Súiⱥcúili is now an in-universe conlang "inspired by" Vegúili, rather than "descended from" it. (Out-of-universe, Vegúili doesn't even exist yet.) This is something I've been thinking about for a while, and it's at least partly as an excuse for the language not being very good as a naturalistic language since it was made so long ago. (Lwaitel, on the other hand, is not an in-universe conlang for that reason.) Despite this, I'm still sort of trying to make this language as I would have back when I started it. Also mentioned the aliens.
#2016-09-12: added some audio, and otherwise mostly reorganized and tried to clarify and edit some; +13 words in lexicon (but none of them are actually new) (583)
Added audio to the phrasebook and to some words (particularly interjections, letters of the alphabet, and proper nouns)