When choosing German as portal language in the setup wizard, the installation sets German as default language. But English is still a required language for content. An English translation has to be added always.
Steps to reproduce:
1) In setup wizard, choose German
2) Create a webcontent
3) Enter a title (Note the German flag/de-DE for the field)
Expected result: Content is published.
Actual result: Error: Bitte geben Sie einen gültigen Titel an.
English is indeed the problem, to confirm: Click the de-DE Icon, switch to en-US and enter some text. The content can be saved.
I checked the usual suspects, instance settings and site settings, but everything looks fine.