Google was not able to help me, so....let me ask one question to German speaking users :

What is "entstordrossel" , as it i announced for 3.9 µH & 1.1 amp it is probably an electronic component , but which one ?
(from Google : "drossel" seems to mean "accelerator"...... )

The word is "Entstördrossel" (noise suppression choke) and a Google search for "entstördrossel in english" finds many translations.

Those chokes can be used between centre rail pickup and decoder and between decoder and brushes (and, as eroncelli wrote, some leave them away).

The diagram shows the analogue three-pole motor (Delta version) with the choke from the analogue locos (you should have seen that in any analogue Märklin loco).
There was only one choke with that type of motor.

Modern locos use two chokes that look like green resistors. Normally they do not appear on the spare part list, neither on the explosion diagram.
You can see them on the explosion diagram for 37542, soldered directly to the brush plate.

The choke represented in 37542 diagram is an old version and made with actual copper wire around a ferrite core (ferrite is a special material with high magnetic characteristics): no special connection, no "plus-minus", simply two end wires.

Nowadays, these chokes look like a resistor, usually green painted, with the same round coloured marks.

In addition, old analogue locos used to have 2 ceramic capacitors (those light brown discs, one between the motor poles and the other between one pole and ground).

With digital decoders, interference suppression is still a problem (mainly with brush motors), but the solution to reduce the electrical noise is technically different, just because of a different motor connection.

In a diagram, chokes should be represented as "coils" (with or without the symbol of the magnetic core, represented by 1 or 2 lines alongside the winding symbol), but sometimes, for non literate, are shown as "rectangles".