Even worse is when you play as Greece and greek people are slowly becoming a minority in their own provinces..I defeated turks as Greece, picked back greek provinces and STILL greek pop was declining....muslim birth rates I guess
It's not an assimilation issue. Just think about it: how turks can assimilate to greeks and vice verse?
Assimilation rate should be really small (through inter-cultural marriages, so few in Victorian era). So it's a good thing that it was decreased in AHD (as I heard).
The actual issue with balkan regions is that they should have really small, almost insignificant turkish population, as it was IRL.
The other issue is crazy pop migration within the country, when annexing back my core regions, I keep discovering that my greek brothers have migrated to Iraq...
Maybe migration "to the core provinces" would be a good idea.
Anyway, balkans are just so poorly implemented in V2 that I prefer to play some other countries just not to disappoint myself (despite my high sympathy to this region and its nations).