Idea: Encourage translations by transforming Duolingo's translation section into a Quora style question and answer service.
(In what follows, the credits mentioned are distinct from those already in Duolingo.)
When writing a translation, you would be able to turn it into a question by explicitly annotating parts of it that you are uncertain about or that you do not want to guess.
You would need to spend a certain number of credits to submit such a translation because it is actually a question that requests help from others.
Whether or not your translation is a question of this type, you could earn credits from it if people rate it highly.
It is also possible to earn credits by fixing up other people's translations with uncertainty and/or omission annotations (thus answering their questions) provided that those fixes result in highly rated translations.
The incentive for earning credits would be to use them to submit questions of this type. Moreover, you could pay more credits to ask certain people to fix a translation and also to promote the translation more widely so that it is more likely someone will help you.