Isn't the Witcher set in a wholly fantastic, non-European, realm? Like, obviously to some degree inspired by European fantasy, but it's not like there's an America to go to and bring back the potato from.
If you hadn't heard of this, there's a lot of press coverage, but here's a petition with 50k signatories. https://www.change.org/p/lauren-s-hissrich-don-t-limit-ciri-...
(If anyone is considering commenting about their opinions on this kind of casting being Good or Bad, let's not – the point is that the Witcher's "historical accuracy" is something people have a lot of feelings about.)