The translation was done by Webcard Forum member Cattss and you can read their announcement on the forum.

There is a detailed explanation on how to use Language Packs in the documentation but it is a very simple process.

• Download the pack from the downloads page and upload it to your “export” directory. Do not unpack the .tar archive.
• Log in to your admin centre and click “Import/Export Language” under the “Languages” section.
• Choose the tarball lang-Francais.tar and choose a name for the language. French of Francais would be the most logical.
• Simply click “import” and the language will be ready for use by your users and administrators.

Big credit is due to Cattss for the excellent translation.