I am a student of masters mechatronics and during my course, I attended many elective management classes. I am even allowed to write my thesis in strategic management and I'm interested to continue my career somewhere in teaching in this field. Am I allowed to pursue Ph.D. studies in Strategic Management after completing my bachelor in Mechanical Engineering and Masters in Mechatronics from German university?
Yes, you are. In Germany, it doesn't really matter what exactly your masters degree was, as long as it's close enough to give you a good background for your PhD studies. Basically, your masters degree should enable you to self study whatever you need to work on your PhD thesis with very little help from your professor. If it does that, then it is close enough.
Now the difficulty is finding a professor who will take you on as a PhD student. With your masters thesis already in the field of your choice, this should be doable despite the different degree subject.