Unfortunately that was not possible to automatically translate from German to English, because these group title is created from the user and these data already stored in database, so when it populate group title on the page, it will load back the data what it stored in database.

Perhaps you can try this translation module so the user can choose which language they want to translate on the current page.
https://extensions.joomla.org/extension/gtranslate/

Hope this will help.