"Are you a farmer?"
Translation:Ffermwr dych chi?
dach chi is a very common dialect variation of dych chi used particularly in north-west Wales in writing as well as in speech. It also appears in the national media sometimes.
This course does not cover many dialect forms, but that one is so common that it has been included.
See the course notes for 'Present 1' - https://www.duolingo.com/skill/cy/Present-1/tips-and-notes