Since President Trump and Kim Jong Un’s summit in June, the two leaders have issued a series of statements in English. South Korean President Moon Jae-in has weighed in too, with vague words promoting hope for denuclearization and a better life for the North Korean people. Yet Mr. Moon tells a different story in Korean.

Consider the speeches the South Korean president delivered in North Korea last month. At a dinner on Sept. 18, he declared he was “truly astonished by Pyongyang’s development.” He didn’t say how this “development” has had any positive effect on the North Korean people. Outside Pyongyang, North Koreans suffer. One third of North Korea’s children are malnourished while the regime focuses resources on nuclear warheads, missiles and luxuries to keep the elites content.

In his speech, Mr. Moon expressed hope that inter-Korean collaboration could “span across the continent to reach Russia and Europe, and across the sea to reach Asean and India.” He made no mention of the U.S. He also told Mr. Kim that if they “put their heads and hearts together,” they will find ways to develop the “military, economy, society and culture of South and North Korea.” Yet some 80% of North Korea’s military, 1.2 million strong, remains forward-deployed, poised to attack. North Korea’s long-range artillery stands ready to strike from the Kaesong Heights.

Mr. Moon also recalled that during his first in-person meeting with Mr. Kim, the two crossed the military demarcation line “hand in hand, like two affectionate lovers.” That’s nice, but since then Mr. Kim has done nothing to reduce the threat his country poses to its neighbor. And he continues to abuse more than 100,000 men, women and children in his notorious political prison camps.

The day after the dinner, Mr. Moon spoke before thousands of North Korea’s “core class,” gathered for a gymnastic and artistic festival. He used Mr. Kim’s exact locution in averring a joint commitment to a Korean Peninsula “without nuclear weapons and nuclear threats.” The truth is that the South has been nuclear-free since 1991. It’s the North that needs to give up its weapons. To Mr. Kim, denuclearization of the “entire Korean Peninsula” means removing South Korea from the safety of the U.S. nuclear umbrella. Mr. Moon effectively announced support for Mr. Kim’s goal of ending the U.S.-South Korea alliance.