Salut @nicolas-picand!
You can download the amp french translation file from the following address: https://www.razz.com.br/amp/amp-fr.mo.
After that, put it inside the languages folder in the amp plugin (/wp-content/plugins/amp/languages).
If you want to make any changes, go ahead and download the po file and use PoEdit to translate or correct anything you need. Remember to save the .po file and to upload the .mo to right folder.
I also made the amp.po file available at https://www.razz.com.br/amp/amp.po.