Accent Human accents are Olde English. However you should speak in modern English but use an Olde English accent. Successfully creating a combination is very convincing in Azeroth.
Speech Humans talk in modern English but don't overdo things. Again striking a balance between the old and new is important. Beware sounding like Shakespeare but don't sound like an American businessman. Example: Three humans are talking about their recent Deadmines raid. Human 1 is right, Human 2 takes it too far and Human 3 doesn't go far enough.
Human 1: That raid was invigorating, eh? Human 2: Yea, that was a highly amusing, slaying that knave Vancleef. Human 3: Yeah man, that was fun and all. We should do it again sometime.
Accent Night Elves have kind of old Nordic and old Germanic very slightly. Ishnu Alah almost sounds Indian. However don't be too strong or you will not be convincing.