I got four ratings now for my app in Germany which are visible on iTunes Connect and the AppStore. The ratings are shown when I navigate to my app in the AppStore and click on "No ratings". Then, they appear.
My App does not show any stars, because it says "There are not enough ratings available". So my question is: What is the needed count of ratings to make the AppStore lists show stars under my app? Maybe 5?
Correct. The answer is as you guessed 5.