Overall +1. But I don't know if I support you pick at will. A sturgian lord owning a Sturgian fief building an Aserai/Vlandian quarter does not at all makes sense. But an Kuzhait lord holding a Sturgian city founding a kuzhait enclave does make sense. Maybe a Vlandian lord serving Sturgia could build a Vlandian quarter. I don't know , I want some connection!
I would like to expand it though! I want different types of enclaves.
The lord can build a military quarter, drafting freemen(recruits) and smithing artisans to the city.
Adding 1-2 weak smithowning artisans of lords or faction's culture. When an artisan dies, of another culture than the enclave dies, a enclave cultured artisan spawns besides a native one.
When implemented, this works quite as OP suggested.
Spawning merchants should have chanse to be of a different culture depending on trade infuences.
Ex, if 75% of trade in a battanian city is done by Vlandian merchants, there should be a decent chanse of a spawning weak merchant of Vlandian culture, besides a random battanian one. He offers Vlandian caravan recruits, mixed with Battanian Volunteers if he becomes powerful. Caravans prefer trading with same-culture merchants so a vlandian merchant gets an extra share of influence provided from Vlandian caravans(Could always be true. In homogenous towns it would not matter)
Spawning criminal gangleaders should have a chanse of beeing of an enemy culture if prosperity is low.
Thinking this could be a cool feature. He spawns besides a native gangleader. If gangleaders becomes strong, they could offer troops of the bandit faction assosiated with his culture mixed with native recruits.
Villiger Landowners I need to think more about.