"How many letters are there in the Greek alphabet?"
Translation:Yunan alfabesinde kaç harf var?
Yes, Yunan is not in genitive, therefore I would say it's a compound noun here. Besides, Yunan doesn't mean the Greek language, it is either a noun meaning Greek (person) or an adjective. It's actually interesting because here it has the role of an adjective but grammatically behaves more like a noun, forming a compound noun with alfabe.