Apparently the Japanese name is an informal term that can mean both "thunder" and "lightning" in the relevant contexts. (As in if you really wanted to mean one without the other, you'd use a different word.)And how come "Thunder" is an electric type move, because last time I checked, it refers to the rapid expansion of heat in the atmosphere caused by a thunderbolt, but NOT the thunderbolt itself, so it should be able to get blocked by Pokemon with soundproof.
The description of the move is unambiguous though, specifically saying that a thunderbolt is dropped onto the opponent. (Funnily enough, the move Thunderbolt is just described as hitting the opponent with "a strong electric blast".)
Agreed with everything about hail though.