Intelligibility
The differences among the dialects are not trivial, and in many cases result in low mutual intelligibility: people who speak one dialect cannot understand or be understood by those from another. Thus by this 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 these 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.)
Read more about this topic: Nahuatl Dialects