A: Thanks for writing. There are multiple different language families of Native American languages. People who speak languages within the same language family can understand each other to varying degrees. So, a Sioux person could probably understand an Assiniboine person. Those two languages are very closely related. Maybe it could be compared to Danish and Swedish-- some words and pronunciations are different, but speakers can mostly follow each other. For a more distantly related Siouan language, such as Osage, maybe it could be compared to Danish and English-- it's easy to see how a lot of words are related if you look, even though people can't automatically understand each other. But for other languages that don't belong to the Siouan language family at all, such as Navajo, there is no relation and Sioux people couldn't understand those languages at all unless they studied them and learned them-- more like Danish and Japanese.
Hope that helps, have a good day!
Native Languages of the Americas
Siouan language family
Amerindian language families