Some authorities, such as the Mexican government, Ethnologue, and Glottolog, consider the varieties of modern Nahuatl to be distinct languages, because they are often mutually unintelligible and their speakers have distinct ethnic identities. As of 2008, the Mexican government recognizes thirty varieties that are spoken in Mexico as languages (see the list below).
Researchers distinguish between several dialect areas that each have a number of shared features: One classification scheme distinguishes innovative central dialects, spoken around Mexico City, from conservative peripheral ones spoken north, south and east of the central area, while another scheme distinguishes a basic split between western and eastern dialects. Nahuan languages include not just varieties known as Nahuatl, but also Pipil and the extinct Pochutec language.
The differences among the varieties of Nahuatl are not trivial, and in many cases result in low or no mutual intelligibility: people who speak one variety cannot understand or be understood by those from another. Thus, by that criterion, they could be considered different languages. The ISO divisions referenced below respond to intelligibility more than to historical or reconstructional considerations. Like the higher-level groupings, they also are not self-evident and are subject to considerable controversy.
Nevertheless, the variants all are clearly related and more closely related to each other than to Pochutec, and they and Pochutec are more closely related to each other than to any other Uto-Aztecan languages (such as Cora or Huichol, Tepehuán and Tarahumara, Yaqui/Mayo, etc.)
Little work has been done in the way of the historical linguistics of Nahuatl proper or the Aztecan (nowadays often renamed Nahuan) branch of Uto-Aztecan.