You will need a browser that can translate French e.g. Chrome. I was able to redeem the key on my mobile.
Enter your email address, answer the Captcha and you'll get a free one month Game pass key.
Better be quick. The Europeans are onto it.
Free trial offer for new subscribers, limited to one code per person.
Non-cumulative codes that can only be used once per Xbox account.
The code must be used before March 31, 2019.