What does the German AZF radio license test comprise of in the oral examination?
There are a lot of differences in the US and European communication.

I got my AZF about a year ago and basically you have to do simulated IFR departure and approach. In addition you will have to fill out an IFR flightplan and answer 30 IFR communication questions.

I would say it is a similar difficulty like the BZF, it might be even a little bit easier, as you just have to repeat what the controller tells you (but you still have to be aware where you are).

An example on how radio communication is done can be found at http://www.caa.co.uk/docs/33/CAP413Supplement.pdf or http://training.ivao.de/trainingsunterlagen.html?tx_drwiki_pi1%5Bkeyword%5D=IFR-Funkbeispiel

I would however recommend a training at a flight school (which costs around 150 Euros).