“Amish” isn’t a language but Pennsylvania Dutch has plenty of written material, although most speakers of it prefer to write in English with the occasional person who prefers German.

I live adjacent to a few thousand speakers of it and I doubt there is a single person over the age of 8 who can’t speak English fluently.

Due to the lack of a standard orthography don’t expect LLMs to do anything remotely usable other than generate a few laughs.