added French translation

[wpdumont]

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Changes proposed in this Pull Request:

Add PO and MO files for French translation

How to test the changes in this Pull Request:

1. add PO and MO files in /languages folder

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you successfully run tests with your changes locally?

Changelog entry

Enter a summary of all changes on this Pull Request. This will appear in the changelog if accepted.

Added French Translation