What language did Karana speak in Island of the Blue Dolphins?

We don't know for sure. At the time she was discovered, linguists could not identify her language. In the fictional book Dear Miss Karana, the main character contacts the spirit of Karana and realizes she speaks a language similar to Chamteela, the tongue of an India reservation in Southern California, 150 miles away from where Karana was found, San Nicolas Island. Some now believe that could've been the closest language to what she was speaking. But as Karana is dead now, we cannot confirm. It will most likely remain a mystery.