You can change the language of your back office in the "My gallery" section under the "Profile" tab which you'll find on the left of your back office space.
At the bottom of this page, you can choose the currencies, units of measure and languages you want to apply to your default account.
You will then be able to choose your default language between English and French and the translations you wish to add as secondary languages. The secondary languages available are: fr, en, es and de. Don't forget to save at the bottom right. If you don't choose any secondary languages, the content will be translated directly with Google Translate.