“Native American languages spoken north of Mexico constituted at the very least two dozen families, with a range of variation across the continent as broad as that on the entire Eurasian landmass, taking in Indo-European, Chinese, Japanese, Arabic, and others.”
Few of those Native American languages survive, and fewer yet will make it another hundred years. “Generally, the last generation of fluent speakers has learned it only partly, never truly living in the language, using it only in the corners of their lives. As a result the language is slightly pidginized.” By pidginized, John McWhorter means simplified. The more complicated aspects of the language, especially those most dissimilar to the replacing language, are forgotten or disregarded. Vocabulary, too, falls away.
So even if there are people alive who know how to speak a language the language may be a shadow of itself, may more truly thought of as dead or, at least, undead, a shambling, half-alive creature that can be pushed to the stage to perform (poorly) on ceremonial occasions.
source: The Power of Babel: a natural history of language, by John McWhorter