In this situation, is it permissible to turn left and then make a U-turn at the intersection?

In the photo, at dusk, you are waiting in a line of cars before a junction with traffic lights; directional traffic lights S-3 on a post on the left, with sign D-6 above them, and a second identical set on an arm above the roadway show a green signal with two arrows - to the left and for a U-turn. In this situation both turning left and making a U-turn at the junction are allowed. The answer is: yes.

The Regulation on road signs and signals states that signals given by directional traffic lights S-3 apply to drivers travelling in the directions shown by the arrow or arrows, and a green signal on such traffic lights means that when driving in the direction shown there is no conflict with other road users. Two arrows mean two permitted directions: a left turn and a U-turn - both movements are free of conflict in this phase, because the signals are set so that vehicles from the opposite direction and pedestrians on the crossing get red at that time. If only the left arrow were lit, a U-turn would be prohibited. You move off when the vehicles in front of you have gone, turn left or make a U-turn from the far left lane and switch off your indicator after the manoeuvre.

Legal basis: § 97 para. 1 and 3 and § 87 para. 2 of the Regulation on road signs and signals