The recent exchange of personal letters between US President Donald Trump and North Korean leader Kim Jong-un and other positive developments have brightened prospects for the resumption of denuclearization talks between the two countries.

But one needs to guard against too much optimism, especially considering the two leaders’ tendency to put rhetoric and showy events ahead of substance.

As things stand, a favorable atmosphere has been building up toward the reopening of nuclear talks between Washington and Pyongyang, which have been stalled since Trump and Kim failed to reach a deal in their second summit in February.

The first palpable sign comes from what both say are amicable correspondence between the two leaders. The North’s state media reported last week that Kim had received a personal letter from Trump, about one week after he sent a letter to the US leader.

According to the North Korean media statement, Trump’s letter had what Kim called “excellent and interesting content,” and the supreme leader, appreciating the “political judging faculty and extraordinary courage” of the US leader, saying he would “seriously contemplate” the interesting content.

Neither the North Korean nor US side gave clues as to the content of the letter, but even considering the two leaders’ habit of resorting to rhetoric and grandiloquence, Kim’s words have raised speculation that the two sides may have exchanged new proposals.

Trump also described the letter he received from Kim as “beautiful” and “very warm,” saying his relationship with him remains strong and “something will happen that’s going to be very positive.”

President Moon Jae-in added to the positive tone by mentioning that the US side informed him that Kim’s letter to Trump included something “interesting.”

What needs to be noted is that the US and the North have been increasing their friendly tone ahead of Trump’s visit to Japan later this week, which will be followed by a visit to South Korea on the weekend.

In Osaka, Japan, Trump is also scheduled to meet Chinese President Xi Jinping, who made a hugely publicized state visit to North Korea last week. Moon likewise plans to meet Xi on the sidelines of the G-20 summit to be held June 28-29.

During their summit in Pyongyang, Kim told Xi that he will exercise “patience” in efforts to resolve the Korean Peninsula issue, while Xi said China will work closely with the North to address the issue.

Echoing all these seemingly positive developments, US Secretary of State Mike Pompeo strongly indicated the two sides could restart talks soon.

Pompeo said there may be a “very real possibility” of the US and North Korea resuming their working-level talks. He went on to say the US is prepared to engage in dialogue with the North at a “moment’s notice” should the North indicate it is ready.

So attention is being given to Stephen Biegun, the US special representative for North Korea, who will visit Seoul ahead of Trump’s June 29-30 visit to South Korea.

The diplomat, who acts as the head of the US working-level team, also indicated a positive move toward the resumption of talks with the North, saying in a forum last week that “both sides understand the need for a flexible approach.”

True, the diplomatic negotiations that had been deadlocked due to differences between the concerned parties cannot make much headway unless either or both sides make a concession. Flexibility may be necessary in this regard, not so much that full denuclearization of the North is put to risk.

It is hoped that all the good words being employed by Trump and Kim translate into actions that reopen substantial denuclearization talks between the two sides.

Without the restart of working-level talks, all the rhetoric and any showy event -- there are media reports and speculation about Trump’s visit to the Demilitarized Zone and even the possibility of a surprise three-way meeting of Trump, Moon and Kim at the border village -- would be meaningless.