Animals not only have to communicate with their own species, but with animals of different kinds. This sort of communication is necessary when two different species of animal live closely together or come together for a special purpose.
Sometimes, one animal depends on another. The former is known as a ‘parasite’, since it exploits the other animal and uses its own language to deceive it. Alternatively, both animals might benefit from their association. In these cases the two species will come to share a language between them, understood by both.
We ourselves try to communicate with other animals. Usually we do this by teaching animals to understand a language that we have devised and which is really foreign to them, like asking a dog to ‘sit’. Perhaps much more interestingly, we sometimes are able to speak to the animal in its own language.