The Nahuan or Aztecan languages are those languages of the Uto-Aztecan language family that have undergone a sound change, known as Whorf's law, that changed an original *t to /tɬ/ before *a.[2] Subsequently, some Nahuan languages have changed this /tɬ/ to /l/ or back to /t/, but it can still be seen that the language went through a /tɬ/ stage.[3] The best known Nahuan language is Nahuatl. Nahuatl is spoken by about 1.7 million Nahua peoples.[4]
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, their grammars differ 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.