We're currently evaluating our plans for how to thank translators. JFBConnect has under 100 strings total, and most of those are pretty short. In comparison to some extensions like JomSocial (with thousands), it's a different ballgame.
We are planning to translate the full admin section, and that may change our ideas of rewards, but until then, the reward is an inclusion of your information in the language file and gratitude for helping others with your contribution. If you have some blog posts or examples of what other developers are offering, we'd love to see them.
We'll keep you posted on what we plan to do as our Transifex project is brand new. Transifex also just started charging for projects, and we're trying to determine how that will affect our translation efforts.
Thanks,
Alex