The problem is, I need both, so if I have a publication in English, I need it to be somewhat like: Birch Y.J., Wood A.D., Oak B.B. et al. Blablabla test // Journ. Test/ ed. Apple S.J. 2020 Vol. 13, Issue 15, P. 100-1000 and the one in Russian must be the same but with all Russian abbreviations (see above), when I saw that there are locales in CSL file, I thought it would work Russian with Russian and English with all the remanning articles (GOST reqs), but something either's not supported or I need to remove that hardcoded part (thx for mentioning!).

Yesterday I didn't find any, though I may need to work and investigate a bit more. I thought locales are turning that into multilingual (btw, according to the docs and tests tag default_locale is not necessary, that's for an author to decide whether include it or not) and also some of Maxim's comments and tags in the CSL file suggest he tried making a multilingual citing style.

Right now, I am diving into CSL docs, hoping to find some hints. If that doesn't work, I will try something else (maybe creating a python script to generate citing list), but for Russian docs that's a huge issue, also some of the journal editors have such strict rules for citations in journals, that editing it becomes an issue much bigger than writing something valuable. I unfortunately even know one such editor who even invented his own style (more complicated than even GOST itself) and that's just a hilarious amount of reqs and rules you have to follow.

I will definitely try my best to 1) update GOST thing; 2) help authors who have to follow the rules; 3) learn as much as possible, given that's an issue, in any case a proper solution is required. I myself and many other authors are struggling, given some serious piece of research, scientific breakthroughs and even proper modern reviews require huge amount of literature to be processed and cited. That's really painful to edit it manually, given you're citing like 200+ refs, even 20 refs... That's not how it should be, I mean, we live in OpenAI age and can't auto-cite all those articles properly, like sorry what?

All in all, I will spend next days coping with the docs and experimenting with the CSL. I will be absolutely glad to share any results and conclusions with everyone. As a coder I will be also more than happy to participate in any development improving free scientific tools for everyone.

I stumbled upon this discussion and can confirm all the conclusions. The style is intended for one language of citations (that can be switched) or for the cases, when the reference list is dominated by either Russian or English ones (the rest can be fixed by Edit Bibliography function).

Automatic language switching for terms would definitely be great, but I am not aware of any progress in this direction. One relevant discussion is mentioned in the style comments (in Russian), but it boils down to the need to use Multilingual Zotero (which is not that common, as I understand) and corresponding CSL-M styles.

In the framework of the regular CSL some ugly workaround may be possible by explicitly scanning the field "language" and updating the terms respectively (at every usage). But that will require all items to have this field filled - I am not sure if that is the case for CSL-M styles in general (alternatively, there may be ways to obtain the item language, say, from the title). Anyway, using the existing capabilities of CSL-M seems more appropriate, but I haven't looked at them.