Based on a quick search, in German the cuts you are looking for are Rippenbogen, Bauchlappen, Dünner Lempen or Flanke. Maybe a German speaker can comment on whether any of these are accurate. You may be after Brust or Nachbrust. It depends on exactly how you define 'skirt steak', as some butchers use the term interchangeably with 'flank steak'. For what it's worth, I've never seen this cut in any Swiss German or German butcher, so I suspect you have to ask for it. Take this picture along with you.

In France, though, the cut is very common. In French, you want to ask your butcher for bavette. They normally offer these in thin slices, but if you ask your butcher he'll give you a larger cut. More specifically, a bavette de flanchet is a flank steak and a bavette d'aloyau is a flap steak. Simply asking for a bavette gets you a piece from one end or the other of the long piece of meat at the bottom of the cow's belly.

It's one of my favourite cuts. We buy a bavette big enough for 3/4 people, marinate it, and cook it on the grill. I buy it as often as it's available in the summer months, but it tends to be hit-or-miss as to whether my butcher has it on any given day.