Even insects have a language, since they communicate with one another using chemicals and body language. All animals have ways of communicating, even if they do not speak with a human voice.
But even the ability to speak with a human voice is not unique to us. A grey African parrot named Alex learned human speech and could answer questions correctly, without hesitation, about objects he had never seen before. This showed that he was not simply memorising answers, but engaging in logical analysis and demonstrating an understanding of abstract concepts such as shape and number. (A video about the parrot.)
The language of some species is far more complex than we once assumed. For example, prairie dogs produce different calls that sound identical to the human ear. Only after recording and analysing them with a sound spectrograph did researchers learn that prairie dogs have a much richer vocabulary than people had imagined. Although the calls sound the same to us, prairie dogs can warn one another whether an approaching person is a man or a woman. They also have different calls depending on the colour of the person’s clothing, and calls that indicate whether the person is carrying a weapon.
People used to complain about racial bias in intelligence tests. Now we have an even harder problem in our tests: species bias. One obvious example is that we often judge animals such as dolphins by how many human words they can learn and understand. Yet dolphins have a very complex language that we have not been able to decipher. If dolphins gave humans the same test, they might conclude that we are completely unintelligent because, despite all our efforts, we have not learned even one word of dolphin language.