Suggestion: Allow learners to translate discussions in Duolingo's discussion forums. A translated discussion would be seen by more learners (which could result in more translations, which would be seen by yet more learners, and so on).
There isn't anything preventing you from translating discussions on your own.
It would be better with an immersion type UI. Such a feature would also encourage people to do this.
Il n'y a rien qui vous empêche de traduire des discussions sur votre propre. =)