I think a common question is, "It says the translation is outdated but why can't I translate it?". I'm thinking about adding this to a FAQ section.
(This is mostly a note to myself, but if someone has time to do it before me - go ahead if you want.)
I don't understand this question. If the system says something is outdated it knows there is an update marked for translation, so why would you not be able to translate it?
I probably remember it wrong then. The situation is as follows: Person A has written a page and marked it for translation, Person B translates it. Now Person A adds some text, but Person B can't translate the new text, because the new version hasn't been marked for translation yet.
So the "It says the translation is outdated" part is probably not correct, the question is why a translator sometimes can't update a translation. (A: The new version hasn't been marked for translation.)
I think you are mistaken. As far as I know the translators only see messages that refer to the version already marked for translation. It's possible to have a development version of a page for some time that does not get marked for translation until the author clears it. In that case the translator sees nothing about it.