I started wondering if the Irish name for the city of York comes from Middle English or Norse, as one might first assume on basis of simple history, or if it's not actually from Latin instead.

I think the city itself goes Eboracum—Eoforwīc—Jórvík—York via several invasions and at least one folk etymology, but I have no idea how it got into other languages. I know the underlying language is uncertain; presumably Brythonic something, but there are no attestations outside of the Romanized place-name.