WPML Translation should be pretty straightforward. You need to login to your site, go to WPML -> String Translation, then from domains dropdown chose gens-raf and translate. You can read fully detailed explanation on WPML site here.
After you finish these translations, there are some that will be missing, those are strings that are appearing in the emails. In order to translate them as well, go to WPML > String Translation and scroll down to the bottom of the page and click on the link "Translate texts in admin screens »". Then, scroll through that page to find missing strings, tick the checkbox and click Apply to add it to the String Translation table. Now you can go back to WPML > String Translation and you should see the string added there.
One thing to note is that when marking an order as complete, WordPress is sending the coupon code email in the language that is set for the admin screen.