What must you do when you see this traffic sign?

Your answer is fully correct.

This traffic sign is a warning sign indicating a sharp left bend ahead. According to German traffic rules, you must reduce your speed before the bend to maintain control and safety. Additionally, you should drive as far as possible on the right-hand side of your lane to allow for better visibility and to avoid moving too close to oncoming traffic.

Indicating left before the bend is not required because the bend itself is part of your normal driving path, not a turn or change of road.

Following these two steps helps ensure safe navigation of sharp bends and reduces the risk of accidents.