Hello Stephan and welcome to the forum, you link helps a lot in seeing what goes on.
Vman, why wedeln was so revolutionary in it's time was that it was the first maneuver done from the hip down excepting the pole plants, which are crucial because they time the rythm of the turns, the faster the poles are planted the faster the turns.
Previously, turns always involved some rotation or counter rotation of the upper body which precluded real fast turns because any rotation had to be undone before it could be initiated in the opposite direction.
You asked about initiation of the wedel turn. May I better tell you how it FEELS before telling you the particulars. Start out by facing your body down the fall line and be determined not to let it rotate either way, it just goes down the fall line square. As you start moving, plant a pole and start a turn and only move from you hips down, but not even you hips. The feeling is this: since your body doesn't move sideways at all but your skis move out from under you, they progressivly go more on edge until they are as far out to the side that they can't go more without affecting your upper body, that is when the other pole plant times the turn in the opposite direction and it feels again that your skis will only go so far out to the side without shaking your upper body.
Now the way it is done. You need to have quite a bit of knee bend so that when the skis are out to the side you still have some bend left. After the first edge set allow the rebound of the skis to unweight you just enough that the body "floats" without moving up, but allows you to transition by moving the skis underneath you to the other side and there is almost no weight on the skis while they do so but they gather progressivly more weight as they move out to the side having most of it at the edge set at the end of a turn. The need for that rebound unweighting is so that a higher percentage is of side to side movement compared to forward movment can take place.
Wedeln can be done with feet together or several inches apart, but they must move independently, contrary to some beliefs, you can't wedel with knees locked.
The modern short swing is an extension of wedeln. Wheras wedeln was done mostly on moderate terrain, the short swing uses progressivley more edge set and brings the skis around more on steeper terrain. Though the short swing stresses a quiet upper body, the neccesity to move the skis more than in wedeln makes it slower in it's execution.
Go on Buttermilk, start straight down aiming your body at something down the hill and don't let it move sideways or turn from there. Make a "walking" movement, putting all your weight on one ski and push it to the side, then, when you feel that the turn would want to take your body out of the fall line,plant your poole and step on the other ski, that's all. The faster you "walk", timing it with your poles, left pole right foot, right pole left foot, the faster your turns will be. Your main objective should be to not let the turns affect your upper body at all.
Clear as mud, eh? ..Ott