feat: add French i18n and fix translation messages

[ymougenel]

Hello,
I added a french translation for the plugin. While doing so I also noticed that some translation properties where not entirely set.
Therefore I moved the properties into the main folder:

Before:

After properties moved:

Testing done

Run all unit tests
Switch the browser between French,English and Japanese in order to check the translations

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[ymougenel]

Please let me know if you see any improving points on this MR :-)

[ymougenel]

Hello, any feedbacks on this MR?

[basil]

Thanks for the PR!