大般涅槃經義記 1.99

1.99

第三呪詞。何故不翻？翻改失用，多不神驗，所以不翻。又復呪詞未必專是天竺人語，翻者不解，是以不譯，諸經呪詞不翻多爾。

Third, the words of the spell. Why are they not translated? If translated and altered, their efficacy is lost and they mostly lack supernatural efficacy; this is why they are not translated. Furthermore, the words of spells are not necessarily strictly the speech of India, and the translators did not comprehend them; this is why they were not translated. The untranslated spells in various sūtras are mostly like this.