Likutei Moharan 48:4/ליקוטי מוהר"ן מ״ח:ד׳

14. {“Then I will turn all peoples to a pure tongue, that they may all call in the name of God and serve Him with one accord” (Zephaniah 3:9).} But in the future, the nations of the world will be tested through the mitzvah of sukkah (Avodah Zarah 3a). <The verse> “Then I will turn all peoples to a pure saphah (tongue)” will then be <fulfilled>. SaPhaH is an acrostic for Sachar Pri Habaten (“the fruit of the womb, a reward”)—i.e., an aspect of sukkah, as explained.

2Also then the “quarrelsome tongues” <will> revert, and the aspect of riv will no longer exist, as mentioned. There will be one tongue, to “serve Him with one accord.” And so then truth will gain power, as is written (Proverbs 12:19), “A truthful tongue abides forever.” In other words, even the idolators will return to “serve Him with one accord.”

3{“If you do good, se’eit (there is uplift). But if you do not do good, lapetach chatat roveitz (sin couches at the door)” (Genesis 4:7) . } This is, “If you do good, Se’EiT”—an acrostic for Sephat Emet Tikon (“A truthful tongue abides”). “But if you do not do good, Lapetach Chatat Roveitz”—an acrostic for RaCheL, backwards. [Backwards indicates that it is] with face turned aside, an aspect of quarrel. She quarrels about the exile, because the nations of the world—“quarrelsome tongues,” “whose mouth speaks lies”—gain power.