Ask HN: How do you Gain Contributors for Localization of FOSS?

As one of the core developers of a FOSS, I regularly think about how to encourage users to switch from a passive role to a more active one as a contributor. In my opinion every user can be a contributor, be it by providing code, documentation or just some useful feedback. And then there are translations.

The software I work on is a project management tool and has already been translated into ~40 languages. Not too bad, right? But I would love to add some more and improve the existing ones, since most aren't even 100% complete.

Currently I just keep a list of contacts of people who provided translations before and get in touch with them before a release. Using LinkedIn or Xing does not seem to work at all when asking for (unpaid) OS contributions. Posts on other social media sites sometimes gain a little traction, but somehow I'm convinced that I'm going about this in a suboptimal way.

Can you help me?

Which ways do you use to attract more translators? Do you use any tools to manage translations? If yes, which ones? Something you wrote yourself?

For the sake of completion, this is the software I'm contributing to: Collabtive --> http://collabtive.o-dyn.de