Literally, the first part of Zephaniah 3:9 reads, “For at that time I will change the peoples a pure lip.” Given the sense of this part of the verse, the ESV is not out of order to supply “the speech of” and “to,” resulting in, “I will change the speech of the peoples to a pure speech.”
9 “For at that time I will change the speech of the peoples to a pure speech, that all of them may call upon the name of the LORD and serve him with one accord.