Only some of our apps have other languages. You can find that list here.
To change the language of the activities, you can go to the Settings in the app (gear icon at the top right of the main start screen) and select the language.
To change the language of the interface (buttons, graphics, etc), you need to change the language of the device itself. You can do that from the Settings app on your device.*
*Note that in Conversation Therapy, you cannot change the language of the interface, only the questions.