Bookable Calendar / Booking Page and 1:1 are currently not available on the mobile apps. To use these tools, use the web version of Doodle.
The language the app will adapt, depends on the language you have selected on your device. If you wish to change the language of the app, you need to change the language of the device first (granted that the language is supported by the app).
The Doodle app supports the following languages: