You want to turn left. Who is required to wait?

You indicated correctly that you have to wait when turning left in this situation.

According to German traffic rules, when you want to turn left and there is an oncoming vehicle going straight or turning right, you must yield to that oncoming traffic. Here, the blue vehicle is coming from the opposite direction and has priority since it is continuing straight.

Even if you have a green light or no specific traffic sign, the general rule is that you must give way to oncoming vehicles going straight or turning right when you are turning left. This is to avoid collisions and ensure a smooth traffic flow.

So, your decision to wait is correct because you must allow the blue car to pass before completing your left turn.