Obviously my question will not lead to a discussion of the problem. So I'm going to add my story to those of wikipedia. I learnt the expression in the German Army in the sixties where it was currently used for special effects during manoeuvres. In my old French dictionary Sachs-Villatte the French noun truc with the general meaning fraud is also indicated as a special theatre expression for machinery used to produce special effects on the stage, eg special transformations. In my view the French military took over this theatre term for their similar devices in manoevres and this term came to the German military as well. But it was transformed from truc over *Trück to Türk, and finally to Türke, a simple metathesis of the sound r. So when a German officer said "einen"man hat einen Türken bauen"gebaut" he meant to produce athe special effect was produced by tricks with specially built machinery and devices. He did not speak of a person from Turkey or a turc who played chess.