Is there any website for professorship positions in Germany? I find few websites, but they don't cover most of the universities. There are more up-to-date advertisements on the website of universities, but it is very time consuming to check them one by one.
I have covered this very recently in the answer to a related question.
Firstly, there is is Academics.com. It is a free service that should have you covered to a large extend. As a bonus, it is not strictly for offers in Germany, but also has some professorships in neighbouring countries (although coverage for those is rather spotty).
The most complete list is the newsletter sent out monthly by the "deutschen Hochschulverband", which is the union of German university teachers. This list is pretty much complete for Germany, but it does not have any info on professorships anywhere else. You need to be a member to receive this newsletter, and one can only become a member by having been employed in an academic post at a German university before. If you currently work in Germany (e.g, as a PhD student or postdoc), you are either already a member or can easily become one.