Complex sentence: For some trains, it is still a stop for changing locomotives, the trains of the Berlin-Warszawa-Express are now operated with multi-system locomotives, which can use both the German and the Polish electrical supply.
Split into simpler sentences: For some trains, it is still a stop for changing locomotives. The trains of the Berlin-Warszawa-Express are now operated with multi-system locomotives that can use both the German and the Polish electrical supply.