Who has to indicate in this situation?

Your answer is correct because both you (1) and the blue car (2) must indicate in this situation.

The explanation is based on German traffic rules regarding intersections and right of way. Here, you are driving in the middle lane, intending to turn left. The blue car on the left is about to move from the left side street onto the main road, likely joining traffic or turning left.

In Germany, vehicles must signal when they change direction or lane to inform other road users of their intentions. You must indicate your left turn to warn the vehicles behind and oncoming traffic. The blue car must also signal, as it is entering the main road and likely turning. The red car, on the other hand, is waiting to turn right onto the side street and does not need to signal at this point because it is waiting, not moving yet.

Always remember: signaling helps prevent accidents by making your intentions clear to others. In intersections like this one, multiple vehicles may need to indicate simultaneously based on their planned movements.