Requirements for getting into a German physics MSc
This seems to be a common misconception: An MSc is not considered a graduate degree in Germany but the second part of an undergraduate study that prepares for the research-only PhD. As such, the universities are required by law to admit all applicants that satisfy the formal requirements as specified in the examination regulations (Prüfungsordnung in German). (The only exception is if the number of applicants exceeds the capacity of the department, which to my knowledge is not the case for physics in most places.)

These regulations vary somewhat between universities and disciplines (and even different courses of study within a discipline), so you really need to look at the one of the specific university you're interested in (or google Masters physics admission $UNIVERSITY, if you don't know enough German), but it boils down to holding a sufficiently successful Bachelor's degree that is reasonably similar to the one offered by that university. What this means depends on the course of study, but as a rough guideline


the degree must be recognized as equivalent to a Bachelor's in scope (number of credits, mostly 180 ECTS) and depth (university-level);
the transcript must show certain courses deemed crucial by the department (the regulations will contain the list of courses, whose contents can then be looked up in the Modulhandbuch);
the diploma must show a minimum grade (again, this will be given in the regulations; I've often seen 3.0 or better according to the German grading system which goes from 1.0 (best) to 4.0 (barely passing).)


In addition, you need to 


show proficiency in the teaching language as given in the regulations (this could be either German, English, or both). Most regulations I've seen also explicitly require a German language certificate 
for the Deutsche Sprachprüfung für den Hochschulzugang (DSH).


Although these requirements will be checked on a purely formal level, there's usually some leeway in the proceedings; e.g, if you are missing some courses from point 2, you might be admitted under the condition that you catch up on them within the first year, and a grade worse than required by point 3 might be compensated for by a brief oral examination where you show that your academic performance from here on is likely to be better than in the past. (But it's important to stress that this is not required if you already meet all the formal requirements.) 

As an example, you can look at the admissions page of the TU Munich (which is regarded as one of the more "professionalized", as these things go).