Original Language?
IMDB shows this as Italian, but when I listen to the English track, the scenes with the English actors don't seem to be dubbed (or if they were, it was redubbing of their original English lines...)
On the other hand, it's set in Italy, signs etc., are in Italian, and I feel that some actors aren't speaking English but are dubbed instead.
I know that many times with these Italian films (horror, western, gialli, etc.,) that they would just film some actors in one language, and others in a different language, then just redub all or most of the film into the release language.
I've even heard that some of these films (or Hong Kong films because of Cantonese/Mandarin) are just filmed without sound, and then dialogue is dubbed in later.