I see a major problem with this. Why would we assume dolphins have one single language? I see no reason to assume their languages wouldn't be as diverse as ours.
But worse still, you have to factor in the decline in dolphin populations over time. Maybe at their natural numbers, there would have be many thousands of dolphin languages, each spoken by tens of thousands of dolphins. But we've severely degraded their numbers. Now each dolphin language is the equivalent of one of those dying indigenous languages that now only has a handful of living speakers. Dolphin language might be a collection of such near-extinct languages, each highly distinct from each other. Maybe there's thousands of dolphin languages, each spoken by only a few dozen dolphins.
And unlike human languages, these dolphin languages weren't replaced by some broader hegemonic dolphin language, a dolphin English, Spanish, Mandarin, etc. There is no dolphin lingua franca that we can train the model on. There's just a whole series of dolphin language remnants, mutually incomprehensible to each other.
This is a real problem because LLMs require vast quantities of data to train on. It may simply not be possible to gather enough samples of a single dolphin language sufficient in quantity to train an LLM on.
Also we should rename the bird to "türkiye."