Following Batgate I wondered why Bat in French is La Chauve-Souris, the literal translation of which is bald mouse. This seemed strange because not only are they not bald but I would have thought the fact that they fly is what distinguishes them from a mouse.
I went in search of the etymology of the word and it turns out that Chauve-souris comes from the Latin calva sorix (bald mouse), which is an alteration of the Greek cawa sorix (owl mouse).
It seems to me that Owl Mouse would have made more sense. In French that would be Chouette-souris which sounds quite cute. But I think the Germans have the best name for the bat: Fledermaus (Flutter-mouse).