After fumbling with the Theme files and trying to hardcode a french version of buddypress-community... I found the "Internationalization" thread which delt remarkably with the issue.
Alas... i tried both the plugin way and the .po file way, none of which succeeded.
On the one hand, buddypress-community doesn't show up in the codestyle-localization items list (fair enough no .po file to be found there i thought...), on the second hand, eventhough i followed the codex poedit's steps one by one i ended up with a catalog update error (no files found in the analyzed directory, incorrect catalog entries...) and no data from the file sources to translate...
I know for a fact that the files actually are coded to be translatable (the _e thing, right?) ... sooo i can't figure it out.
Does anyone have a clue? Better still : anyone with a packaged french .mo file for buddypress-community?