Several articles have made me look up some SharePlay features, and this is what I found out:
(source: http://faq.en.playstation.com/app/answers/detail/a_id/9993/~/shareplay-on-ps4-and-its-limitations)
Germany
• German PSN account holders can only use Share Play with other German PSN account holders.
• The visitor is required to input a German ID number before joining host’s Share Play session if the game is 16+.
Other limitations (full info in the link provided):
Share Play cannot be used:
• If the game which you want to share is not available in the PS store of your visitor’s country.
• If the Parental Control Level of the game which you want to share doesn’t match the visitor’s Parental Control Level setting.
• If the visitor’s age is lower than the game’s age rating on the PS Store.
I guess the main reason is Germany's strict censorship policies, which in the past have caused some games to be heavily edited, or even completely banned (Dead Rising comes to mind...)
