So I went ahead and tried it myself and it is driving me insane 
While I assumed it would be straight forward, it doesn’t seem that the direct translation of the English translation is working in German for this endpoint type. The lack of German utterance examples in the Alexa developer API documentation doesn’t help on top of it.
At this point, I am not sure what to recommend for your issue. You can try to use less common words to see if it makes a difference.
In the meantime, I have opened a case with the Alexa developer support team. Let’s see what they come back with.
The way you are providing the information below is fine. You don’t need to include the screenshot. Just include the item name and its label should be fine.