I am the person named in user12956's answer and have been active with the German-language plagiarism documentation site VroniPlag Wiki for the past 4 years. I do apologize for the English-version of the home page disappearing, I'll see what I can do to get it back.
This is indeed not a legal issue, as copyright claims have to be made in court and the chances of getting anything happening in this area in Germany are almost zero. Going through the university is indeed the only way to go, and unfortunately, as some have noted, they are not all happy to hear about cases like this. I have informed universities about over 120 cases of plagiarism, so perhaps I can offer some perspective here:
- The first question is: is this a doctoral thesis or a bachelor's or master's thesis?
- If it is a doctoral thesis, then it must be published in Germany. It can be found in the university library or the German National Library (DNB). The person to contact is the dean of the department that granted the degree. I get marginally better response rates by CCing the president/rector on my email. But in over a third of the cases I did not even receive an acknowledgement of my email (that includes careful documentation), so I had to ask back two weeks later.
- If it is a bachelor's or master's thesis that happens to be published, then I would also contact the dean, but not CC the president.
- If it is a bachelor's or master's thesis that is not published, you will need to contact the Prüfungsausschußvorsitzender, not the Prüfungsamt. Trying to find this person will be very difficult, as German university web pages are in general not in English and/or up to date. The idea of contacting the advisor or having your advisor contact someone at the university is excellent.
- The Ombud people at universities or Ombud der Wissenschaft (no longer only for DFG-financed projects, but for all cases) tend to get involved in authorship disputes, data ownership disputes, and the like from within the university. They are generally not equipped to handle plagiarism accusations, as they have practically no resources. Some university ombuds will try to keep you at bay by requesting things such as a translation of your thesis or additional documentation. They, too, generally have no resources.
The problem is that German universities do not have honor boards or even a collective notion of what constitutes good scientific practice and how to deal with academic misconduct. Often it will indeed be classified under data privacy laws, although most universities indeed have a process codified that includes telling the informer what their decision was and giving reasons. But even I, a known German researcher in this area, end up writing letter after letter trying to obtain knowledge about how the university has dealt with a case that I informed them about years ago. I've just published a paper together with a colleague about this miserable situation: "Viel Licht und noch mehr Schatten – Wie Universitäten auf Plagiatsdokumentationen reagieren". In Forschung & Lehre, 4/2015, pp. 278-280.
There is no central German body to which you can apply, and I don't have the time or resources to investigate all of the many cases that show up. If the case involves a published dissertation, then it is possible for you to document it on the VroniPlag Wiki site. There are theses in German, English, and Spanish documented on the wiki. There would have to be at least one other scientist who reads Russian, though, as the cases must all be verified before they are made public. But since it is an open platform, it is possible for someone to be found who can verify this. There is no "magic" software that is used, and translations are not (easily) discoverable with software anyway.
If the university does not answer you, you can send documentation of your attempts to get the university to take action to the Kultusbehörde of the German state the university is in and ask politely what you need to do to get the university to answer you. This can indeed get the university to wake up. But don't do this until you have tried honestly to get information from the university.
It is not the job of the university to prevent plagiarism. The universities in Germany operate on the (unfortunately no longer valid) assumption that students learned how to write and do research and understand mathematics in high school ("Studierfähigkeit"). The universities should become more proactive about plagiarism prevention than they currently are – many just purchase software and figure they are done. They don't realize that software is only a tool and both identifies non-plagiarisms as plagiarisms and misses blatant copy & paste. I have tested such software since 2004. They need policies and they need to communicate them and they need to teach the students how to be good academics. But all this costs money, and the universities are trying to save money where ever they can. I don't want to excuse them, but help you to understand the problem.
I do encourage anyone who is confronted with something like this to take action – eventually, one hopes, the German universities will wake up to the problem and begin to deal with the very serious plagiarism problem that present today.