I had already checked out your repository because that's of course the first thing one would do when setting up a new web service, and I fixed a bunch of obvious issues in the French translations while I was discovering your web interface.
Since I'm not really interested in creating yet another account on yet another web service, I won't be submitting these fixes through Transifex; you'll find them in this pull request so that they aren't lost entirely, and so that one is able to do the needed extra work to get them merged.
This is rather unfortunate:
Unfortunately we can't easily make it possible to allow changes on github, but I've done those changes on transifex now, so your work isn't lost.
Thanks Stefan, much appreciated; I'll head to Transifex directly if I see further updates that could improve piwik's l10n.