Update to French translation

Stephen,

I have updated the French language files. At the same time, I have done 3 corrections to the "admin_tab.php" file: changing "Languange" for "Language".

There currently are 42 untranslated strings left, and I don't think I can translate them soon. A few of them relate to totally new functions; most of them relate to new themes (i.e. those that were not included in Zenphoto). Therefore, I would need to experiment a lot to make sure I find a proper translation.

Therefore, as I saw that you had a target of late August for the official release of Zenphoto20 1.0.0, I think you could consider that this translation is the one to be published with v.1.0.0. Maybe you could publish a warning, like a week before, so I can check for late corrections (in the English files) that would need last-minute updates of the French files.

Regards,

Michel Gagnon