Within this section of the advanced settings you will be able to define what language you want email notifications such as reminders or invitations sent from Mailtastic to yourself or colleagues.
You can get to this feature by clicking on the gear icon at the bottom left corner of your screen, click "Settings." Then click "Advanced Settings" and select "Email Notifications." There you will be able to choose if you want the language of the email notifications to be in English or German.
Then you are all set!
