Principal English Translation:
for something to be restored or satisfied (see Molina); to prosper (see Karttunen); or, for something to come into its own, be as it should be
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), 222.
Alonso de Molina:
ixtlaui. (pret. oixtlauh.) restituirse osatisfazerse algo.
Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 48v. col. 1. Thanks to Joe Campbell for providing the transcription.
Frances Karttunen:
(I)XTLĀHU(I) to be restored or satisfied, to prosper / restituirse o satisfacerse algo (M) [(7)Bf.Iv,2r,4v,6r,9r,9v,12v]. This has the same sense as (I)XTLĀHU(A) used reflexively.
Frances Karttunen, An Analytical Dictionary of Nahuatl (Norman: University of Oklahoma Press, 1992), 121.
Lockhart’s Nahuatl as Written:
often but not necessarily with on-. synonymous with and often paired with pōpohui. Class 2: ōixtlāuh. intransitive counterpart of ixtlāhua. 222
Attestations from sources in English:
popohui ixtlahui = to flourish, come into one's own (central Mexico, sixteenth century)
Personal communication, James Lockhart, in sessions analyzing Huehuetlatolli.