German locale & English CP language resulting in disappeared entries
From the docs:


  The default language that the Control Panel should be rendered in, for users that haven’t specified their Preferred Locale.


defaultCpLanguage is only applied for users that don't have a Preferred Locale set in their user profile.

Your entries disappeared because you don't have any entries created in the English locale, yet.  You might need to enable en under the Section's settings before that's an option.