There's no way around it: Dolphins have big ol' brains. When you combine this neuroanatomical truth with a given pod's advanced social behaviour, the animal becomes a natural candidate for studying cognition in the animal world. In particular, the desire to understand structure and breadth of a dolphin language has gnawed at researchers for upwards of forty years.
One such research group, led by Denise Herzing, has developed a rudimentary interface that allows researchers to teach wild dolphins man-made whistles for various objects—say, seaweed or rope—and then translate dolphin whistles back to English if an animal repeats the 'word' for a given item. The device is an analogue to the kinds of keyboards that non-human primate researchers have traditionally used to chat with chimps.
It's important to keep in mind that the interface doesn't decode dolphins' natural sounds. But science will be science, and other groups are working on that.
Here's a question: What kind of variance does Herzing's group observe across dolphins' repeats of a given sound? That is, how confident are the researchers that their interface isn't forcing a translation onto an otherwise innocuous whistle?
And does the interface have an accent?
Herzing is very careful about how she communicates with and understands dolphin society. "In that sense it is a bit like being an anthropologist. You want to observe and understand a culture before you start interacting with that culture. I constantly worry about 'dolphin etiquette' in the water and over the years we have learned what not to do, to show respect and understanding for their rules as much as possible."