You are right to say that the first question we must ask is what is meant by 'language'. One of the fundamental marks of language is that words have 'non-natural' or conventional meanings. If I raise a hand to strike someone, that is not a statement in a language but a natural sign, just as dark clouds are a natural sign of rain. Of course, we can exploit natural signs, we can convey thoughts and meanings by leading others to make inferences from our behaviour. This connection can be further developed.
All animals communicate.
Pack animals especially have evolved elaborate signals that establish a hierarchy of command and facilitate co-ordinated action. These are covered by the broad term 'instinct'. Some animals have shown a capacity to innovate, for example apes and chimpanzees. The innovations exploit 'natural' meaning, in the way indicated above. There are limits to what one can get across in this way.