Human languages exist to compress the world around us in a way that will survive being sent over sound waves and uncompressed in another brain that experiences a similar enough world around them.

Meaning that with enough words and their relations, sufficient complexity forms for its processing to result in intelligence.

Remember that an AI can process far more textual data than we can. It is still orders of magnitude smaller the amounts of information we process through our senses, but it is still a start.