The name 'Calanais' is the correct Gaelic equivilant for the English name 'Callanish'. It is derived from the Norse, and is not used as often as the anglicised name (also derived from the Norse) but it <i>is</i> correct.
I must admit I've never come across the term <i>Calanais I</i> before. The site is sometimes known as Callanish I, but this name is usually (but not exclusively) used by first language English speakers.
As I understand it both 'Callanish' and 'Calanais' are pronounced in similar ways anyway. It's a bit like the Welsh word for 'taxi' (tacsi).
:-)#
K x