My idea for it to be hyper-localized, so that it is different in each language.
It is a common convention of poets and the like to write something in to the tune of
You are the ___
You are my ___

The translator would either make something like that up, or find something with expired copyright, possibly changing it a little.

Then in the comment field of the string, each translator provides their string, and back-translation.

"Norwegian Bokmål: Du er en nattens sol.
Back-translation: You are the nights sun." (makes sense because of the midnight sun)

To ability, it does push the boundary of how creative translation can be, as with making up new words etc.