I've just started playing and it's very clear that Niko is Serbian.
1.Nikola Belic - pure Serbian first name and last name (it would be Bijelic or Bjelic if it is from Croatia, Bosnia or Montenegro)
2.Niko and his cousin at the beginning mention that they hate albanians, which are current serbian sworn enemies for taking Kosovo out Serbia.
3.Niko mentions that he was in a war few years ago - the only war on that territory in last few years
was on Kosovo between serbs and albanians
3.In very short time i've heard a bunch of serbian senteces from him:
"Zdravo burazeru" - at the beginning of the game, meaning "Hi bro"
During small car accidents you can hear Niko often saying:
"Ti si imbecil" - "You are an imbecile"
"Ti si djoka" - "You are a dick" (rarely used in serbian language with that particular word, but that IS a literal translation...someone has been using a dictionary instead of hiring additional staff
"Moronu" - "Moron"
The problem is a very lame interpretation and ridiculous accents - cause even completely serbian sentences doesn't sound serbian at all (more like russian or something)...they probably spared some money hiring a few general eastern europeans to deal everything...for god sake, at least for your main character you could've found serbs willing to help for free
Issue with Bellic instead of Belic is also just a pure rockstar mistake
- there is no eastern european lastname with double L
- all eastern european lastnames that ends with "ic" are pronounced "ich", so no serb, croat, bosnian, russian, bulgarian or anyone similar would've pronounced it "Belick" (like they do in the game), but "Belich"
...thats about it for now and i'm sure i'll see a lot more serb stuff and a lot of just wrong stuff by the end of the game.
However, I doubt that Rockstar will ever announce Niko's nationality since they probably already know that they did a very bad job, so they might just say that they wanted it to be a mistery or somethin...