What is the right course of action?

You have chosen correctly to allow the blue car to turn first. According to German traffic rules, when multiple vehicles approach an intersection like this without traffic lights or signs, the vehicle going straight or turning right usually has the right of way over a vehicle turning left.

Here, the blue car is turning left, and you are also turning left but are approaching from a position that requires you to give way. The motorcycle on the left must also give way since you are not directly facing it, and it must yield to the blue car going first.

So the correct order is to let the blue car proceed before you. This rule helps avoid collisions and organizes traffic flow by giving priority to vehicles closer to the center of the intersection or moving straight before turning left.