Looks like you're right! I found the OP photo on a website called "transphoto". It's a Rathgeber M5.65 from 1965. It was in use in Munich before it was sent (sold?) to Bucharest in 1998, along with more trams of the same make, like no. 2518.

I couldn't find out a lot about this model. The Wikipedia entry about trams in Munich only has a very short section about the M series, and all I could find were a couple of German websites that look like they have marginally more information :c