20 Things You Didn't Know About Layer Cake
6. The Serbian Gangsters Actually Speak Romanian
Marcel IureČ™ briefly appears in the movie as ripped-off Serbian drug dealer Slavo, and while to the layperson he's convincing enough in the part, IureČ™ is actually a Romanian actor, and even speaks Romanian with the members of his outfit.
You haven't got a hope in hell of noticing this unless you're either Serbian or Romanian, and as such it's resulted in a handful of miffed Serbs and Romanians taking their complaints online.
Quite how this discrepancy wasn't straightened out before shooting is anyone's guess, beyond Vaughn assuming so few people would ever actually realise the mistake.