It's not that simple. LLMs are great for predicting next word, but this needs a more unsupervised approach.
Ultimately, you need to know the environment of whales. Sure, you know the next probable token, and even relationships between tokens, but how do they relate to what whales are doing?, in other words what does it mean?.
It reminds me of the great quote by Feynman: "look at the bird"[1]. You can know the name of a bird in many different languages, but that tells you nothing about it. If you want to understand birds, you need to look at it and see what it's doing.
If we want to communicate with another species, we need to understand what they're doing, why they're communicating, and from there we can begin to infer what they're communicating. It could be simply a callsign/identification/name for each individual, it could be communicating you've found a place with food, it could be communicating about predators, who knows. There could be all sorts of interesting variation and nuance to their calls. But ultimately it's necessary to look (in the general sense of having information about what it's doing -- could be through all kinds of sensors!) at the ~~bird~~ whale :)
[1] Feynman tells the as a lesson from his father. (that you can know their names and still know nothing about the birds themselves).
https://www.youtube.com/watch?v=ga_7j72CVlc
Bonus related video!: https://www.youtube.com/watch?v=M1TiXLGqlM4