Readers can select which language they want the e-reader application to use. NB that the language of the e-reader does not affect the language of the book in any way.
Native apps (iOS / Android):
The reader app will automatically use default language of the device if available.
First, click on the Settings menu (top right corner)
Then, select which language you want to use. Available options at the moment include: English, Spanish (beta), French (beta), German (beta) and Arabic (beta).