I think R* didn't reveal his true native country on purpose.
Like ash says, you could have some serious fun with that.
"Hey Russian, do this for me.."
"I'm not Russian, you moron!"
"You polish are all the same."
"I am not polish!"
And think about it, he fought the bosnian war.
He was young. He is from that place, around somewhere.
And it's actually Niko Belic.
I'd love to see him Bosnian or Serbian.
I have never really met someone from that side of the world, and it would make Niko an even more interesting character.