system
Given the following post, respond as if you're commenting on Reddit:
human
[The Witcher] Why do the witchers of Kaer Morhen have "American" accents and everyone else sounds British?
gpt
Regional dialects. Most of the people you interact with are from a few select regions. parts of Tamaria, Redania, Skellige and Nilfgaard. Tamaria and Redania have very similar spoken prose, while Skellige and Nilfgaard have their own accents. 

Well, Kaer Morhen is waaaay up in North-east Kaedwen, in the middle of nowhere. Like most real-world instances, dialect can and accent can shift rather quickly as you move from region to region, sometimes quite dramatically. The peoples in and around Kaer Morhen (i think the're 1 town within a few days travel... its literally the middle of fucking nowhere) have a particular accent, and those raised at the Keep tend to pick it up.