Cetacean Intelligence (there's a section for communication).

It's actually really cool too; Dolphins all have something that researchers call a "signature whistle," which seems very similar to the concept of humans each having a name. And the crazier thing is, for male dolphins, a part of their signature whistle will be taken from their mother's signature whistle, while female dolphins have completely original signature whistles. So this shows not only language, but also suggests culture.

Another awesome example; there are two dolphin species, one generally lives further north while the other lives further south, but they both reproduce around Hawaii. When they meet up around Hawaii, they hunt with each other. The two species generally have vocalizations and hearing abilities that are in a different frequency range, but their frequency ranges have some overlap. So when they hunt together, they switch to making sounds that are in a frequency range that they can both hear/vocalize in. So essentially, they're using a bridge language that neither typically speaks when they're separate.

This next study, I've sadly not heard any updates on, but this company is trying to use ML to translate dolphin language. (they were supposed to have finished the study in 2021, but I never heard more about it. Hoping COVID didn't wreck it.)