I haven't played GTA IV yet and thus have not heard Niko Bellic's curses in a foreign language, but if it really is Russian it would be rather inconsistent with his character. He is supposedly from somewhere in ex-Yugoslavia, and is probably a Serb, Croat or Bosniak. So either he's cursing in Serbian/Croatian/Bosnian and you've got it wrong or the creators couldn't find someone to provide swear words in his native tongue and resorted to Russian as the next best thing. Which it isn't. It's like having an American character swear in Dutch and pretending it's English and hoping no one will notice!

Had to repost up in here because I'm no cunning linguist, but I finally learned that he wasn't speaking Russian, but it appears Serbian. (Hey, I did throw out a disclaimer in the original story).

As an afterthought: One more thing that I've since done that I totally should've included in the original story -- I got into an accident and called 911. Got an ambulence and everything. Man, I'm such the responsible citizen.