What is the right course of action now?

In this situation, the correct action is to reduce your speed because the vehicle ahead is slowing down and signaling to turn left. German traffic rules emphasize the importance of maintaining a safe distance and being ready to react to changes in traffic flow, especially in city environments. By reducing your speed, you ensure you can stop safely if necessary and avoid endangering yourself or others. Overtaking is not appropriate here, as turning vehicles or cyclists may pose additional risks. Maintaining your speed would also be unsafe since you might not be able to stop in time if traffic ahead slows or stops suddenly. Always adjust your speed in response to the traffic situation to ensure safety.