Séverin, thanks for reporting this issue
I've updated the language packs on moodle.org and installed a new pack (bn).
As far as I know, all installed language packs should be updated each time a site is upgraded. As moodle.org is updated regularly (it's currently 1.9.3+) this should mean that language packs are kept fairly up-to-date. I'm just wondering why you thought that the language packs hadn't been updated for at least 2 months...
Regarding updating the language packs on demo.moodle.org, I'm reassigning this issue to Eloy to do so. (I obtained a permissions error when I attempted it!)