1 Answer

From the early 20th century to at least the mid-1980s, educational policies in Mexico focused on the hispanization(castellanización) of indigenous communities, teaching only Spanish and discouraging the use of indigenous languages.^[39] As a result, today there is no group of Nahuatl speakers having attained general literacy in Nahuatl;^[40] while their literacy rate in Spanish also remains much lower than the national average.^[41] Even so, Nahuatl is still spoken by well over a million people, of whom around 10% are monolingual. The survival of Nahuatl as a whole is not imminently endangered, but the survival of certain dialects is, and some dialects have already become extinct within the last few decades of the 20th century. http://en.wikipedia.org/wiki/Nahuatl 

This leads me to believe that since it is a language that appears to be one that Mexico wants to abandon, it would not be a language with great emphasis on accurate translation. On the wiki page, it is also stated that the language itself has gone through many transformations. This makes it a difficult language to learn. I would think this would also make it difficult to translate accurately to English.