Well animals do not speak but they use their own language that is incomprehensible for people.
I think that if they do not use a spoken languase they would rely in other forms of communicationscommunication since it is a basic need. They could communicate using signals and drawing using their hands like deaf people do considering that your civilization is the simplest possible. Hunter-gatherers could use this to communicate with each other in a efficient way and they would pass it to the next generations.