After some search in various books in a book store by rapid leafing through them and noting the possible names mentally I made another search online and finally found the name of the similar plant:
It's a Hyssop (in German: Ysop )
This plant is rather new to our region, but due to the climatic changes with milder winters and hotter (and dryer) Summers it feels "at home" here now too. It has been cultivate in more Southern and Eastern regions as early as the 16th century.
Here the photos I took:
And finally as a sort of reminder the "Common Sage" (Wiesensalbei), so they don't get mixed up (although both have their leaves used as a flavoring herb):