I think, especially since this is an alternate history mod, that we are giving a bit too much thought to "realism" and what culture "represents", rather than its gameplay effect.
One effect of culture is to increase revolt risk and war exhaustion in non-culture provinces. Another is to make religious conversion more difficult. Finally, all income from that province, and things based on it like troop recruitment, is lower.
So I think we should assign cultures to provinces and nations based on that. Culture is EU's form of "conquest friction" - every non-state culture province conquered is worth less than a state-culture one, limiting the areas where conquest is cost-effective. (Speaking generally of course - if a player is going for a WC, such a thing won't stop him.) Furthermore, places that should be more difficult to hold on to for certain empires should be differently cultured.
Places where this is done well (in my opinion):
France - the combination of French, Breton, Occitan, and Burgundian clearly limit France's and the French minors' expansion.
Iberia - Occitan and Iberian both keep the northern area an annoyance for Al-Andalus, with the Iberian states revolting quite a bit when Al-Andalus gets in trouble.
So cultures should be placed to 'guide' the AI in its expansion, as well as to give players interesting choices (such as Brittany's parliament event lines).
One effect of culture is to increase revolt risk and war exhaustion in non-culture provinces. Another is to make religious conversion more difficult. Finally, all income from that province, and things based on it like troop recruitment, is lower.
So I think we should assign cultures to provinces and nations based on that. Culture is EU's form of "conquest friction" - every non-state culture province conquered is worth less than a state-culture one, limiting the areas where conquest is cost-effective. (Speaking generally of course - if a player is going for a WC, such a thing won't stop him.) Furthermore, places that should be more difficult to hold on to for certain empires should be differently cultured.
Places where this is done well (in my opinion):
France - the combination of French, Breton, Occitan, and Burgundian clearly limit France's and the French minors' expansion.
Iberia - Occitan and Iberian both keep the northern area an annoyance for Al-Andalus, with the Iberian states revolting quite a bit when Al-Andalus gets in trouble.
So cultures should be placed to 'guide' the AI in its expansion, as well as to give players interesting choices (such as Brittany's parliament event lines).