For participants, the interface and navigation buttons, as well as activation emails are available in the following languages: English, Dutch, German, Spanish, French, Portuguese, Italian, Russian, Polish, Swedish, Czech, Lithuanian, Slovak, Romanian and Hungarian. Participants can set their language preference when activating the app, or from the in-app settings menu post-activation.

Push notifications, email and assessment content is configurable by users directly in the Castor platform in the language of their choice.