To change the language of your account, go to "My account" in the upper right corner and in the drop-down select "Settings".
How to do it in the web version?
Under global preferences, click on the default language and you will have the options available to change your language.
How to do it from the app?
The option to change the language of your account is only available on the website.
In the mobile application, the default language will be the same as the one set on your mobile device.