You can change the language for the edX platform to English, Arabic, Spanish, French, or Mandarin on the Account Settingspage.
To change the language, sign in and then click the down arrow next to your username (in the top corner).
Next, choose Account. You set the Language about half way down the page.
Your new language preference is saved as soon as you select it, and the Account Settings page reloads to display in the selected language.
Note that this setting changes the language used for text that is supplied by the edX platform. Text supplied for individual courses may not be available in multiple languages.