Principal English Translation:
already (see Lockhart and Molina); when
Alonso de Molina:
ye. ya. aduerbio de tiempo.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 34v. col. 1. Thanks to Joe Campbell for providing the transcription.
Andrés de Olmos:
vale tanto como ya del castellano
Andrés de Olmos, Arte para aprender la lengua Mexicana, ed. Rémi Siméon, facsimile edition ed. Miguel León-Portilla (Guadalajara: Edmundo Aviña Levy, 1972), 186.
Lockhart’s Nahuatl as Written:
"Somewhat similar to o, although it belongs even less to the verbal complex, is the particle ye, 'already.' Often it need not be translated; it simply reinforces the sense that something occurred in the past. ye oquiz in tonatiuh = The sun has (already) risen." (p. 35)
"much used with anything past, also with imminent events. in ye iuhqui, when things are ready" (p. 242)
James Lockhart, Nahuatl as Written: Lessons in Older Written Nahuatl, with Copious Examples and Texts (Stanford: Stanford University Press and UCLA Latin American Studies, 2001).
Attestations from sources in English:
This word was originally ya, but changed over time to ye, just as miac or miyac went to miec or miyec. But in Tlaxcala, we find ya enduring more.
Here in This Year: Seventeenth-Century Nahuatl Annals of the Tlaxcala-Puebla Valley, ed. and transl. Camilla Townsend, with an essay by James Lockhart (Stanford: Stanford University Press, 2010), 56.