Update French translations

The French translations seem up-to-date on the Transifex platform but not in the Git repo.

And I would like your opinion about the "Append" and "Insert Next" translations.

Currently:
- Append --> Lire à la suite
- Insert Next --> Ajouter juste après

I suggest:
- Append --> Ajouter à la fin
- Insert Next --> Insérer juste après