Nahuatl is the language of the Aztecs, and other Central Mexican peoples. At the time of the Spanish conquest it was easily one of the most widely spoken native languages of the Americas, with a geographical extent from what is now the northern reaches of Mexico to the southern border of Nicaragua. It continues to be widely spoken in Mexico and ranks as the most common native language in that country, with approximately a million speakers. It is part of a larger language family called the Uto-Aztecan family that includes North American Indian languages such as Shoshone and Ute, spoken as far north as Montana.
Schwaller, John F., "FLARR Pages #23: Nahuatl Contributions to English and Spanish, Part I" (2001). FLARR Pages. 23.