What is the difference between "is" and "hath"?

Revelation 9:11 And they had a king over them, which is the angel of the bottomless pit, whose name in the Hebrew tongue is Abaddon, but in the Greek tongue hath his name Apollyon.

whose "name" in the Hebrew tongue "is" Abaddon

but in the Greek tongue "hath his name" Apollyon

What is the difference between "is" and "hath", referring to his name?

Why does it say, "but", when mentioning Greek?