As others have noted, the use of the accents reflects the need to place accents based on current Spanish speakers' pronunciation. The rules of Nahuatl dictate something different. In many place names ending with -tlan or -tan, modern pronunciation places the stress on the last syllable, thus needing an accent in the rules of Spanish. But this is not the case in traditional Nahuatl pronunciation where the accent was ALWAYS on the next to last syllable (yes, except for vocatives and a very few other instances). So, in general I do not use accents on Nahuatl words.
The mission of the H-Nahuatl network is to provide a simple medium where scholars interested in studying the Nahua or Nahuatl (Aztecs or Aztec language) can go to be in communication with others. The network will accept postings in English, Spanish, Nahuatl, and French. Historically the network has addressed issues relevant to understanding nuances of Nahuatl, the grammar and structure of the language. It also serves as a place where the general public can inquire about specific issues of the Nahua. Lastly, it provides a forum wherein scholars can announce their research plans and seek assistance from others in the field.
The samples you mention, Some examples are Teotihuacán, Tenochtitlán, Copán, Chichén Itzá, Uaxactún, Kabáh, and Yaxchilán.
are accented for Spanish. Nahuatl speakers would say Teotíhuacan, tenochtítlah (the "n" is nasalized and hardly, if at all heard) etc..... I do not know about the Mayan words.
If your press wants to give readers a version of the original indigenous spoken word, I would argue for the samples I have shared.
If you are wanting to show how they are said in modern Spanish, then there would be no need to change the orthography.
In the case of Tenochtitlan, the Nahuatl pronunciation was "Tenōchtítlān", stressed on the "i", but because the last vowel is long, Spanish-speakers hearing it rendered it as "Tenochtitlán", because standard Spanish does not have long vowels.
What are the current standards for placing diacritics on Nahuatl and Mayan words? Are there rules in place, and are these rules different in contexts of English or Spanish? I remember that the penultimate syllable of Nahuatl words is commonly stressed, so it would be redundant to place an accent there. But there are other terms in which I sometimes find an accent on the final syllable, sometimes not. Some examples are Teotihuacán, Tenochtitlán, Copán, Chichén Itzá, Uaxactún, Kabáh, and Yaxchilán.
Your comments will help me create a standard to use by Oxford University Press.
This artilce discusses the discrimination that Nahuatl speakers suffer at the hands of monolingual Spanish speakers in Tlaxcala"