Game concept
Culture Intermingling
From the game's encyclopedia
The more of two Cultures that coexist in the same Realm, the more intermingling will happen and the Cultures will increase their Cultural Acceptance.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Culture Intermingling is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "The more of two Cultures that coexist in the same Realm, the more intermingling will happen and the Cultures will increase their Cultural Acceptance." It is part of Culture. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.