Maybe those German privacy activists going after google et all might want to look at this.
Putting more legislative hoops in place means HR will just need to find more creative ways to formulate job requirements in order to exclude certain classes of people or more creative ways of justifying not taking you application further, but ultimately won't solve the core issue.
It's effectively illegal to complain about employees in Zeugnis, but they can reorder words and skip some phrases to imply that you're a bad employee. If you're not German you might even think you got a good Zeugnis because it looks well on the surface, but there's the entire code you need to learn to read these.
or maybe you ned some high profile sackings of HR directors at a few big German companies ala github.