The Hebrew word for “speech” in Scripture often means “language” (Genesis 11:1, Genesis 11:6, Genesis 11:7, Genesis 11:9; Psalm 81:5; Isaiah 19:18; Ezekiel 3:5–6). The use of the term here to speak of a “pure speech” quite likely refers to the speech of the Gentile nations, which had defiled their lips by the worship of false gods but will have their speech purified as they offer the purest of praise to the one true God.
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.