the prop pitch of the 109 has only 3 positions now

[Strike]

If I understand your question correctly; What is prop feather? The answer is you turn the blades so that the propeller blade airfoil chord is paralell to the airstream, they produce the minimal amount of drag possible, and prevents the propeller windmilling. Picture this: you hold your hand flat out of the window of a moving car, if you hold your hand vertically, you will feel the force of the drag very well, but if you tilt your hand so it's horizontal, there's a lot less drag.

That is what prop feathering does to your propellers. You adjust the blades angle to produce the minimum amount of drag possible. Typically used for gliding after engine loss, or generally on multi-engine aircraft to lessen drag caused by an engine loss.

In modern day airplanes, often the engines start with the prop in feathered position to avoid creating thrust.

In german I believe the prop-pitch panel is marked "Segel-something" and means "Sailplane" mode sortof and intended for gliding incase of an engine stop.