Wikipedia says, "Differences exist in usage of the common terms turtle, tortoise, and terrapin, depending on the variety of English being used; usage is inconsistent and contradictory. These terms are common names and do not reflect precise biological or taxonomic distinctions."
So it should perhaps not be surprising that many other languages use one name for all chelonians - possibly distinguishing, if necessary, "land chelonians" from "water chelonians" by using a descriptive adjective or noun.
Eh, we learnt in the school that it is very strict... this is how you can trust them :D Even in my language (HU) there is an originally definite difference between land and water chelonians ("teknős" vs "teknőc") but nobody cares now—even I don't know which is what :D ) (I think that "teknős" is the water dwelling one. I should ask one of them, perhaps they're knowing...)