[Translations] French translations fix

Fix the French translations based on the English ones.

- I personnally feel `Enregistrer` more natural than `Sauver` or `Sauvegarder`, that is why I made this modification.
- Other modifications concern typo, better translations and consistency (for instance in the Tags section, `objets` to `éléments` which was used previously).

Please, feel free to discuss about any specific point.