Have you heard about Librarians becoming smarter in 1.20.2 (starting from preview 23w31a) Well this means that Librarians are now limited to selling books based on what biome they are set as.
This plugin gives you that functionality to other versions of Minecraft that do not have this option and may never recieve it in the vanilla game as well. There is no configuration since it does one job, that is to make the trades match with 1.20.2:
