Cyrillic could be sorta-achieved if you edited anims.j2a to change all of the letters. It would be tedious work though, and you'd wind up losing most of the latin alphabet in the process.

Being able to type special characters (like the first post suggests) would be a good idea though. A lot of the characters are already in JJ2, and almost every language that isn't english uses some of them (with some languages you can do fine without them, but in others they are pretty important). I'm not sure why St. Louis thinks this is such a bad idea, other than that he seems to think everything is a bad idea.