1. SS isn't that large community to be divided. Smaller language groups will most probably contain 3,5 members and respective activity.
2. Difficulties. Those subforums should have some structure to function well both inside itself and be properly connected with main structure. That is harder, than most user think.
3. MODERATION. It is luckily if at least one moderator able to read each subforum language. And if not?
1. I have Mechwarrior online forum as an example. Its peak number of players in Steam is around 1500 at average (last time i checked it). This forum indicates peak number of forum visitors equal 300-400 at average. Only small part of players visit forums (i think, it isaround 15% of players base), but ok, it will be higher for SS because of some reasons. May be 2x...
MWO forum russian branch some active forum users. I dont say it is hundreds, but a hundred? It seems so... And while i agree that regional section here will have small number of users, i dont think it will have like 20 times less members. Also add here some players who wanna say something, but cant, because, as you said it, translate from russion to english is harder. And imo, 15-20 estimated forum users is OK number for regional section.
2 and 3. Head moderators can choose regional moderator from those, who wants to do that. Then users can organise their section as they want to. MWO forum works just like hat. Regional section doesnt copy the basic structure of forum. It has like 5 sub-sections to categorise some threads (like "for newbies" or "mech loadouts"), one topic for game news updated on regular basis and some topics for trash-talk.