I'm native French speaker and for my fellow french speaking friends/acquaintances i'm a really good English language user (i wouldn't say speaker but reading, listening and writing). I'm really above average and i can tell you that Delver is a world even i never heard of.
First time i saw the "leak" Delver wasn't a word i knew off. I knew of to delve and i made the connection, but even "to delve" isn't something people around me would know. Those are not common words. We would either use "to dig", or "get into" or "jump in" or stuff like that.
So i can clearly say that is it's really the name of the next expansion, you can bet a lot of people with just say "wtf delver even means". Delver sounds like the name of a new character or something.