There's no written record of German's commenting on the effect that Highland regiments had on them because they lost. History is written by the victors. I firmly believe that the Germans feared the Scot's.

-They probably didn't know what to make of the Highland psychological warfare.

-I've heard historians say that WWI Kilts were bullet proof, by shere chance. That's probably why they checked under the kilts. (It's supposed to be noticable in WWI footage, the bullets bouncing off kilts that is.)

-There's a story about a Highland officer who caught his kilt on barbed wire, removed the kilt to preserve the tartan, and continued with combat scaring the $%^ out of his German enemies. In other words he was wearing no bottoms at all.