Thank you for the kind words, I’m happy to help!
Translating text depends on the text you want to translate. The thread link you posted is how to change the text on the Auth0 login form that appears on wp-login.php (or in shortcodes/widgets). That’s related to the “Lock Internationalization” link I posted above. Changing the text anywhere else (error messages during login, settings page in the admin, etc) requires using the gettext function as we don’t have a German translation for the plugin text.
Hope that helps!