There are considerable differences among varieties, and some are mutually unintelligible. Pellicer, Dora; Cifuentes, Bábara; Herrera, Carmen (2006).
Huasteca Nahuatl, with over one million speakers, is the most-spoken variety. "Legislating diversity in twenty-first century Mexico".
Canger (1988) tentatively included dialects of La Huasteca in the Central group, while Lastra de Suárez (1986) places them in the Eastern Periphery, which was followed by Kaufman (2001).
At the conquest, with the introduction of the Latin alphabet, Nahuatl also became a literary language, and many chronicles, grammars, works of poetry, administrative documents and codices were written in it during the 16th and 17th centuries. Today, Nahuan languages are spoken in scattered communities, mostly in rural areas throughout central Mexico and along the coastline. Mexican Indigenous Languages at the Dawn of the Twenty-first Century. This article focuses on describing the general history of the group and on giving an overview of the diversity it encompasses. For details on individual varieties or subgroups, see the individual articles. "Nahua in ancient Mesoamerica: Evidence from Maya inscriptions". Regardless of whether the Nahuatl is considered to label a dialect continuum or a group of separate languages, the varieties form a single branch within the Uto-Aztecan family, descended from a single Proto-Nahuan language.
Within Mexico the question of whether to consider individual varieties to be languages or dialects of a single language is highly political. In the past, the branch of Uto-Aztecan to which Nahuatl belongs has been called "Aztecan". From the 1990s onward, the alternative designation "Nahuan" has been frequently used as a replacement especially in Spanish-language publications. As a language label, the term "Nahuatl" encompasses a group of closely related languages or divergent dialects within the Nahuan branch of the Uto-Aztecan language family. The Mexican Instituto Nacional de Lenguas Indígenas (National Institute of Indigenous Languages) recognize 30 different individual varieties within the "language group" labeled Nahuatl. Most of these loanwords denote things indigenous to central Mexico which the Spanish heard mentioned for the first time by their Nahuatl names.