A few weeks ago I had made a relevant suggestion titled "Assimilation and Multiculturality" which didn't see any interaction:
https://forums.taleworlds.com/index.php?threads/assimilation-and-multiculturality.436800/
As it is the game is very monotonous and monocultural. Even North Korea has a couple foreigners every now and then, but all towns are culturally uniform and static.
Below is the text of the post I linked:
As it is the whole culture thing in the game is pretty static. A nice addition would be the following two game mechanics:
1) Assimilation
If a settlement stays under another culture's hold for long enough a time (like a couple decades), slowly the notables change cultures. E.g. Battania took Lageta and held it for 30 in game years. Assume there are 5 notables. After that time, one by one, notables convert to Battanian culture, and the troops they provide change to Battanian trees. Battanian items pop up in the marketplace, and locals start dressing up like Battanians. Sometimes, randomly, the town's tournament is Battanian style, and as time goes by, like say in 60 or 70 or 100 years Battanian culture takes over. Same for all cultures. You could even add translations of all settlement names for each culture so that say after 100 years in game there's a chance that Lageta becomes, say, Laghaith (could even be an algorithmic change).
Tangentially, it'd be neat if the player could rename settlements that belong to their clan.
There could also be relevant kingdom policies like 'Elite Dominance' where the conquering kingdom forces their culture. It'd have loyalty and prosperity penalties but if the clan can offset that the conversion is slightly faster. If they fail this would accelerate rebellions, which would be a nice little combination.
2) Multiculturality
As it is, settlements have notables only of settlement culture. This looks and feels very artificial. It'd be nice if there was a random chance esp. towns would have notables from other, mostly neighbouring cultures. Their troop trees would still be of local cultures, but if Assimilation is implemented, these would be the first to convert if the conquering culture is same as theirs.
E.g. Varcheg neighbours Battania. By random chance it has one Battanian notable. The notable gives Sturgian recruits (but maybe also Battanian ones every now an then, rarely??). Now imagine Battania takes Varcheg over and holds it for say 20 years, kicking off a Battanification process. Then the said notable quickly begins to give Battanian recruits.
IMHO these two features in combination would make the game map way more lively and dynamic and realistic. As it is, it's always the same old, same old, and it gets boring after some time.