It’s not necessarily unique to Germany as similar beliefs about witches turning into wolves are also found elsewhere like England and Italy to some extent. What’s remarkable however’s that it seems to be a common enough theme in German thought to even have an Anglophone book published about it. It’s called Lycanthropy in German Literature.
There’s even a chapter specifically dedicated to this. Like I said, it’s not that the belief about witches turning into wolves’s necessarily uniquely German as it’s found elsewhere in Britain and Italy but given Italy’s more directly subjected to German influence longer (though sometimes indirectly and intermittently so), it’s predictable that this belief’s likelier to show up more often there.
It also helps that the author in question also translates stuff so that gives him an advantage in knowing where it’s coming from.
fynm 