They say a lot more in that 'call to prayer' than just a call to pray. Since it is in Arabic, they think the Infidels will not know the difference.
In Israel they would yell, "It's two o'clock. How many Jews have you killed today!?" during their 'call to prayer'. Which actually fits in a way. Islam is a religion of death, murder, rape, and war. So saying that fits right in with Islamic so called, prayer.
I wouldn't doubt that they are saying something similar to that in Germany.