I have never heard their language, but have heard it described. I imagine that to the untrained ear it would likely sound like gibberish.
Author James Michener wrote one of his long historical-fiction novels, "The Covenant," about South Africa. In the early chapters of the book, he describes in great detail the Hottentots and other indigenous peoples of the region - fascinating stuff, how they lived their lives and interacted. Then the story moves on to settlement and colonization by Europeans - first the Dutch Boers, and then the English. This is an incredible book, probably Michener's best in my humble opinion.