I noticed that sometimes Alp Arslan turns Persian (from Turkish). What are the general conditions that make one ruler to change a culture? (different culture of demesne/councillors/wife.../their vs his stats...?). just curious
That second event's also a decision, I think.
culture conversion can happen:
-event which allows you to swap to the culture of the people you're ruling
AFAIK all it takes isp you having your court in a county not of your culture. A decision will always exist in the intrigue tab, nothing else is required, except maybe some prestige cost, not sure there.
there is no such decision (check - william the conquerer/ hautevilles of sicily etc etc...)
the only related decision in intrigue menu is when you are culture A and your liege is culture B - to convert in culture B