Sometimes that can get political. If you want to start a flamewar in a group including both Germans and Poles, ask them if it's "Danzig" or "Gdansk".
(Or just look at the Wikipedia talk page archives for the city.)
(Or just look at the Wikipedia talk page archives for the city.)
Try Czech: Cáchy, Trevír, Řezno vs Aachen, Trier, Regensburg.