It might be, that the game font does not include Cyrillic letters, thus will show only blank spaces.
For me, I would really like to know from developers, if it would be possible to change the games fonts on file level or if we had to re-draw those original.
Like when we did the translation of Neverwinter nights and Neverwinter nights 2, there were separate font files we could changes, where in TES IV: Oblivion and other games (like Darkest of Days) we had to re-drawn original font bitmaps.