I've never seen "vise" outside an American context.

You are wrong about "between" and "among." Again, language is what people use, not what grammarians dictate. It's a distinction that I try to maintain myself, but there's also a distinction to be made between "it's wrong" and " I don't like it."

Ahem: a treaty between western nations, or a treaty among western nations...?

Between you, me and the gatepost, or among you, me and the gatepost?