Catan - Mixing German base game with English extensions and expansions
Per se it should be possible to mix german/english or in your case serbian/english editions. But you should have a close look which edition you're buying (also depending on which edition you already own) there are even (minor) compatibility problems inbetween english editions (this should apply on german editions too)
Also hava a look on this answer.

Besides the form factor english editions of the game have those (in my eyes ugly) white borders around their tiles. Additionally other graphics are used (in my opinion those are shrill compared to the german ones)

I hope I could help you slightly.