You hit the subject directly on the head. Isaiah says that Jehovah will "sift the nations in the sieve of falsehood...." The Gileadi translation explains this.
30:27–28 Behold, Jehovah Omnipotent coming from afar! His wrath is kindled, heavy is his grievance; his lips flow with indignation, his tongue is like a devouring fire. His breath is like a raging torrent that severs at the neck. [He comes] to sift the nations in the sieve of falsehood; with an erring bridle on their jaws [he will try] the peoples.
Because Jehovah’s coming “from afar” is preceded by the king of Assyria/Babylon’s coming “from afar” (Isaiah 5:26; 10:3; 13:5), one event is inextricably linked to the other, implementing Jehovah’s deliverance and destruction. While the righteous receive Jehovah their God, the wicked get a false god (Isaiah 10:12–14; 14:13–14; 37:23–35). Personifying Jehovah’s wrath, grievance, lips, indignation, tongue, fire, breath, etc., the archtyrant cleanses the earth before Jehovah comes. As a new Flood, he desolates all except Jehovah’s people affiliated with Zion and Jerusalem (Isaiah 8:7–8; 10:28–32; 36–37).
[He comes] to sift the nations in the sieve of falsehood; with an erring bridle on their jaws [he will try] the peoples. In the interim before he comes, Jehovah lets all kinds of untruths prevail among his people and the nations to test their loyalties. Persons who keep his law and word—the terms of his covenant—intuitively know and accept the truth, while those who wallow in sin can’t perceive it and stumble. People conditioned to deceiving themselves (Isaiah 28:15; 44:18–20; 59:3–4) fall prey to the deceptions of the archtyrant (Isaiah 10:7; 21:2; 33:1, 7–8)—the sieve of lies and bridle of error.