false prophet
I don't know how old that saying is, but it would be interesting to see if they used it in the middle ages. In those days almost anyone from a different religion would be considered a heretic. Maybe the idea of false prophet and heretic were not too far apart.
From recent religious commentary:
Brill 2010 Sibyllinische Orakel 1-2
There's also the possibility of walschen/welschen (which).
I don't know how old that saying is, but it would be interesting to see if they used it in the middle ages. In those days almost anyone from a different religion would be considered a heretic. Maybe the idea of false prophet and heretic were not too far apart.
From recent religious commentary:
Brill 2010 Sibyllinische Orakel 1-2
There's also the possibility of walschen/welschen (which).