What is considered a good GPA for studies in Germany

Given that "grade inflation" is often much less rampant in Germany than in other nations (it is not unusual, for instance, for the majority of students to fail an exam in a core subject), the standards inside of Germany tend not to be as stringent as in other places I've seen. For instance, anything better than 2.0 (on a 5.0 scale, not a 4.0 scale!) would generally be considered "competitive."

Obviously, there are limitations—if you get a 2.0 because you've gotten 1.0's in the general courses and 3.0 in the courses in your subdiscipline, you're not likely going to be an attractive candidate to an outside group.

However, I think much more important than the exact GPA is the quality of the master's thesis. If you have a very strong master's thesis, you will likely get some interest from the group in which you did the thesis work to continue on for a PhD, if there is an open position available. A weak grade on the thesis (anything below a 1.3) usually is a sign of substandard performance, which is likely to result in not being considered for a position, even if your GPA is a 1.1 or 1.2 (it's unlikely to be a 1.0 under such circumstances).

I am doing a PhD in a graduate school funded by the German Research Foundation and I was graded 2.0 in my master's thesis (mainly because it was written in English and my grammer was not 100% perfect). What I am trying to say, is, that beyond just the grade of your master's, it can be important to have some kind of experience in the respetive field of your desired PhD. In my case, I was holding several positions as a student assistant in my former university. Also first publication experience might come handy (even though I would not like to support this ongoing trend). It would likely not help you, to score very high on your GPA but having no (work/research) experience beyond studying.