Well, since the question was updated (and other issues arose), I updated my answer.
First of all, I am not sure whether using Russian language in questions and answers at all is allowed by higher-level Stack Exchange rules/policies1 (you should understand, that not the whole Stack Exchange is community-driven; hosted sites are, but top-management also exists). If it is, then this discussion makes sense. If it isn't, then current discussion makes sense only in the context like: "Should we allow Russian language with our local rules/norms, if higher-level Stack Exchange rules/policies would allow it someday?"
Second, my original thoughts were not about trilingual site, but rather about allowing every language (I had written that draft for local rules/norms before I realized I am not sure whether it's allowed by higher-level rules/policies). My idea was something like "Ukrainian is strongly preferred; you are allowed to ask in any language — with some languages the probability to get answer is drastically lower — still you may try"). If we're talking about giving Russian some special status among other languages, I'd rather say "no"2.
Sorry for those who have up-voted my answer (before I changed it). You're free to revoke your votes (or even vote it down).
My original answer goes here:
That's my opinion:
TL;DR: I don't see how we can forbid other languages (and Russian, despite all political issues, is one of them). However, I think users should endeavor to write in Ukrainian. Maybe, political preferences will come out anyway (e.g. when seeing question in Russian, some users will expressly answer in Ukrainian, even having advanced level of Russian and theoretically not knowing a level of questioner's ability to understand Ukrainian), but we should not encourage that.
- What I know/suppose about internationalization state of Stack is the following:
- Some time ago Stack was open to non-English languagesprove.
- In 2015 that was suspended; since then creation of new non-English sites is allowed only in those languages, into which Stack Overflow (flagship site about programming) is already localizedprove; as for now, these are four languages: English, Portuguese, Japanese, Russian, Spanishprove.
- Sites devoted to language learning have additional right: to use target language within questions and answersprove.
Although Russian language is in the list of allowed languages (en, pt, ja, ru, es), that still doesn't mean that we will be allowed (to allow) to use Russian in questions and answers. Because:
We initiated as (English) site for learning Ukrainian language. I assume that chance of success in this case is much higher; although pt, ja, ru, es are allowed for consideration, creating new non-English site seems to require explicit permission. And, in any case, it will look like we're changing our initial direction.
"Rebranding" us as Russian site for learning Ukrainian language, per my opinion, will automatically change list of allowed languages (within questions and answers) from English+Ukrainian to Russian+Ukrainian. Do we want that?
"Rebranding" us as Russian site for learning Ukrainian language, per my opinion, will automatically change user interface from English to Russian. Do we want that?
Otherwise, if we go neither as (English) site for learning Ukrainian language, nor as Russian site for learning Ukrainian language — we don't follow any of existing formats (which will surely require special permission).
- In 2016 that was restricted even more: they don't accept non-English sites for nowprove.
- "I'd rather say 'no' [to giving a special status]" — that's actually my vote as one of members, not as initiator. You may vote in other way and, if community wants, I'd happy to participate in trilingual (or other format) site. But I personally prefer: either all-languages-are-allowed, or Ukrainian-and-English-only (I don't see a reason to specially allow/forbid Russian; I don't really care if Russian language will be here; but I don't see a reason to give any language special status [except English which seems to be special for technical reasons]).
So, my opinion is:
We shouldn't forbid any languages by our local norms/rules. But they (except eng, ukr) most certainly will be forbidden by higher-level rules.