I mean you can try find a laywer or two to do so, they will happily try to help you sue void (it's their job after all). Remember that you can lose too, you'll have to pay the laywers for that.
But I mean, what are you going to sue void on? The game is not released yet.
Plus you'll be getting your name in the credits and a free for DLC + one or two extra things (forgot what it is), you've got a mousepad if you're saying you're backer since the first minute, and you've also got the FBI pack.
If you're afraid that VOID aren't working on the game, I can confirm they are, really hard. I don't have any way to prove it because of NDA, but they are.
I am not sure what verbraucherzentrale means either but from what I know about the German culture as someone who visits Germany about every 2 years is that they try their best and love when everything is perfect. A game needs to be worked on to be perfect or close to perfect, we can only wish we could create a f...