Hello! I hope I can be of some use to you!
I currently do the Magister! The interview is intense...but quite fun and challenging. You will almost definitely be interviewed by Greta Bosch....she is absolutely lovely and will really calm you down before your interview so don't worry. Don't stress about not being able to speak the language well enough in the interview, just relax. I am no where near fluent, and I got through my interview. In mine I was given a few scenarios and asked to try and apply legal reasoning (it's not written in front of you so you have to listen). I also found out during my interview that I had a place...they basically tell you (though not exactly explicitly). I didn't do A-level law and no knowledge of law was needed at all!
I hope that helps you a little :-)
(When she tells you your language skills are wonderful and that you won't have any problems with the course...unless you're completely fluent in German, she's lying btw!)