The Atlanteans to communicate under water? In the comics and cartoons they just pretty much talk normally but I really cant see that working in live action, two ways I think they can do it is:
A: They talk telepathically
B: The Atlantean langue sounds similar to dolphin/whale song.
Personally I would love if they went with the whale song idea but that would mean they would have to sub it and they might be reluctent to do that. What do you guys think?