Zweifacker sounds like doublefucker for German ears, it is "Zwiefacher" = double one; after every two bars the metrum changes |:1/2 1/2 1/3 1/3:|

Most famous German example of 5/4 is Prinz Eugen. The song was written after the storming of Belgrad (in the Balkans) during the Turkish wars. The stress changes depending on the flow of the text, mostly 12 123 or 123 12, sometimes 1 12 12