Hi there!
Thank you for bringing this to our attention. Let me clarify one thing.
WooCommerce emails are sent based on the site language (or email language settings), not the customer’s IP address or location. So even if the customer is in France, the emails will be sent in the language configured on your store.
To help resolve this, please check the following:
Go to:
WordPress Dashboard → Settings → General → Site Language here make sure site language is set as Français
If that does not work, could you please share System Status Report which you can find via WooCommerce > Status.
Please use https://pastebin.com/ or https://gist.github.com/ and share a link to that paste in reply here. Once we have more information, we’ll be able to assist you further.