Old Castithan language
Old Castithan is the name I gave to the proto-language that gave birth to the Castithan language. When I initially conceived of the Castithan language, I had this idea. I knew about the history of the Castithans, as invented by the game company (Trion Worlds). All the races were based on one of the seven deadly sins, and a lot had had a major change in their recent history. The Castithan had had a change for the negative, becoming imperialistic and inventing a caste society where there wasn't one before. I had this idea that a lot of their words may have changed meaning (quite intentionally) due to a radical change in culture when they conquered the Irathients and Sensoths on their home planet (or, starting in later seasons, when they invaded Irath and named it Casti—something that happened because a writer thought up the line and show runner Kevin Murphy liked it).
Bearing that in mind, let's jump back to 2011. I've been an avid World of Warcraft player since the game came out, and back then I was captivated by a mechanic that was relatively new to the game, but is now quite common. Death knights had a passive ability where using one move (Obliterate, for the curious) had the ability to allow you to cast another spell (Icy Touch) that you couldn't cast otherwise. You could only cast it when you got the opportunity to do so after casting Obliterate. I thought that was really cool, and thought it would be neat if it worked in a language.
Back to Castithan, given these two radically different stages of the language, I thought, what if there was something to trigger a jump to the old version of the language? That is, something that happened that only licensed, but perhaps necessitated a return to the older form of the language? As an alien language, it might be something I could pull off, but it needed a reason.
The way I envisioned it was if there was a radical change in the language due to some event (as it would turn out, the invasion of Irath), there would be a time when those who spoke the language would constantly be negotiating two different sets of vocabulary (imagine suddenly using the word Товарищ "comrade" a lot after the Russian Revolution, or using "Freedom Fries" because the Republicans decide the French are no good for some reason). It'd be a bit difficult at first, but would probably be pretty easy to maintain in public. The time that a speaker would slip would be in informal situations, or highly emotional situations, when they stop trying to be polite and start speaking from the spleen.
Now, in addition to the basic vocabulary, there was a radical change in pronoun usage. Specifically, the old pronouns stopped being used, and were replaced with new ones (or, to be safe, no pronouns at all). This came hand-in-hand with some other large changes, like pronunciation changes on par with the Great Vowel Shift, and grammatical changes, such as the loss of the original definiteness system. Imagine being a child growing up in this environment. They essentially had two different forms of the language to navigate. The result is that the younger ones interpreted things in a rather novel way. They learned this older form of the language the way that kids on the playground learn swearing—and they treated it roughly the same way. As they grew up with this basilectal form of the language, they indicated—or licensed—its usage by using the old pronouns. That is, once the pronoun had been used, the gloves were off, and they dropped into the older form of the language—or, as it came to be called, Skalanu, or the Flood Form (corresponding to the flood of emotion one feels when swearing).
How long could something like this last? Probably not very long. Think about how English speakers use "thou" or the "-st" and "-th" endings on verbs. We don't really know how to do it; we kind of have a vague collective memory of what Shakespeare kind of sounds like (at this stage not close to accurate). It's also a bit like irregular forms. English had a lot more irregular past tense forms at one point in time, but they get whittled down as the words get used less and less. Eventually this phenomenon would disappear from Castithan, but at the time of the show, it was still alive and well for Castithan adults (e.g. Datak and Stahma), even though it wasn't strong in the younger generation (e.g. Alak).
As a result of this specialized function, the older forms of many words and the grammar of Old Castithan is preserved, somewhat. I used the Flood Form a lot in the show—probably because Datak does a lot of angry yelling and screaming. Not every single word has a Flood Form, though of course every word has an etymology. For that reason, Old Castithan is only partially preserved, and only partially described. Nevertheless, I have quite a bit more information on it than I do some of my other proto-languages.