I've been thinking a little bit lately about how language changes and evolves over time through different coincidences (particularly thinking about Castilian Spanish and the royal lisp), and I got to imagining what a language-focused CK2 campaign would look like.
So you start off with your standard language, and then make changes to how your characters talk based on significant events or such that happen over the course of the game.
A thertain ruler ith born with a lithp, and hith nature demandth that the populathe follow hith lead with regardth to thpeech. Diththenterth are put to the death for mocking their liege.
Then after ein paar yearth of dealing with German thilk merchantth, the nobility pickth up a few German wordth through their tailorth, and it thuddenly becometh thehr moderne to thlip them into converthation.
A couple genewationth of inbwed kindew latew, and the boy-king thuffewth fwom whotathithm, thuth thparking a new vewändwung in the day-to-day thpwache of the uppew claththeth.
It sounds funny in my head, but I can't imagine things getting very far before everything falls completely apart and becomes wholly indecipherable.
I wish it was easier to mod in combination and fracture cultures. I still sometimes find that cultures tend to blob pretty hard, and sometimes there's interesting mixtures that I feel like should create new cultures, but they don't because Pdox never thought of them.
It's one thing for German to push into Polish or even replace it, but if a German count somehow inherits, say, Andalusia, there should be some interesting things occurring.
Stuff like: if the ruler is of a foreign culture, but holds no provinces of his own culture, his culture can't spread to the peasantry (outside of events). If he does, it's at a very slow rate, unless the capital of the country is in one of those properly cultured provinces (e.g. when William conquers England, Norman is unlikely to replace Anglo-Saxon in any province, particularly before English pops). Instead, rulers should be slightly more prone to adopting local culture rather than the other way around - probably over a generation or so though. Childhood events maybe?
Likewise, if a ruler is of a foreign culture, and a combinatorial culture exists, if the realm capital is
not matching culture with the realm ruler, than combinatorial culture events should be more likely to pop than usual. If a normal combinatorial culture doesn't exist, there should be a system in place to create one, either via decision or event. The ruler could even be given the opportunity to name the culture, like with babies. I could even see a slight procedural generation system in place with lists of phonemes tagged with cultures to make sure the name sounds "correct" even when randomly generated.