The rules are as open to change as the data I guess, but if there really isn't one obvious "proper" name I've seen things named with a slash like "name 1/name 2". Often there is specific tagging to overcome this, though. For example in bilingual countries like Wales many roads have any English and Welsh name. The language-specific names are uncontroversial, but the overall "name" (for the international map) is supposed to be in the "local language". As you can imagine this isn't always uncontroversial.