You mean he just overwrote one of the supported languages with his own Russian translation?
Anyway, when testing for the movie text, I noticed that in my (English) version the game has no problem with having two lines in the same translation bloc linked to "0" (the English language recognition modifier).
So I guess someone could for all text files just add his own translation, place "0" as the language in front, and have at it. That is, long as this someone uses the extra "0" modifier after the English translations.