I'm not convinced that "there is a 'universal' language: mathematics and physics".
Physics (as we know it) is a way humans talk to humans about our own activities, as well as about the universe in general.
Dolphins, like humans, are hunters of fish. Yet, as you've mentioned, we've so far been unable to understand dolphin communication.
A smart life-form on another planet might do various other things that humans do, including (for instance) reducing silicon dioxide to elemental silicon in order to then do something with the silicon.
But would that necessarily mean we could understand the way they talk to each other about what they are doing?