Bulbapedia has translated what was said in the trailer about Iris and Dento:
Iris: Iris is wild-acting girl who likes to climb trees and chew berries. For some reason, she's travelling with her friend, the dragon type Pokemon Kibago.
Dento: With an abundance of knowledge and experience, Dento is a "Pokemon Sommelier", who checks ("diagnoses") the compatibility between a trainer and their Pokemon, gives them advice on how to become better friends. Is the actual condition what is expected?
So Iris is basically a wild girl, kind of like Sapphire from Pokemon Special/Adventure like Shiny_missingno noted. Also they didn't give a reason for Iris to be traveling which has me asking a few questions. Is she a trainer? Is she isn't, is that why she carrying Kibago in her hair, because she doesn't have a Pokeball for it? Could it be possible they might try to import Belle's story to her and have her father not wanting her to go on a Pokemon journey?
As for Dento, honestly I heard a few bit of classes of trainer before and would say some are ridiculous... BUT POKEMON SOMMELIER!!! Are you kidding with this? They couldn't come up with a better term for someone who goes around seeing if trainer's are compatible with their Pokemon (which seems a bit jerkish if you ask me) and try to help them get closer? Also, being the Poketch has an application which does the same thing, are we to take that means the next gadget after the Poketch for Generation V won't have that certain applications or any at all? I mean sure it won't help you if your compatibility is low, but it does at least tell you how high/low it is. I have a feeling when we meet him he's probably a beginning "Pokemon Sommelier" and will say something like Ash and Pikachu don't have good compatibility or something.
So I think the main question here is why is Iris traveling and whether Dento will be joining Ash and Iris through Isshu. And if Dento is joining them, what does this mean for Brock or are we going to have another 4-people crew like in Hoenn?
