Wow… thanks a lot for the help… one can’t guess it indeed…
one more tip : when on translate.wordpress.org, beware that the translations for your language may be not validated yet. The default export link exports only “current” translations, i.e. validated ones. Use “Only the matching filter” option and you will be able to export all the messages.
use the “file” unix command to check the content of the .mo file. e.g.
$ file wp-content/languages/bbpress/bbpress-fr_FR.mo
GNU message catalog (little endian), revision 0, 732 messages
by using the default export, I was only retrieving one message, and thus nothing was translated…
