In Star Trek VI, we have this odd (but amusing) quote
"There's an old Vulcan proverb: Only Nixon could go to China."
Why did the Vulcans have this proverb?
This was address (tangentially) in a footnote in The Autobiography of James T. Kirk (2015 written by Kirk himself and edited by David Goodman.
EDITOR’S NOTE: This is a well-known Vulcan proverb, but its origin is unclear. It derives from the events of 20th-century Earth, when President of the United States Richard Nixon opened diplomatic relations with Communist China. The meaning of the proverb refers to the fact that it was considered a political success because of Nixon’s career history of being a virulent anti-Communist; as such, none of his opponents could accuse him of being “soft” on Communism. It is unclear, however, what Vulcan was a student of Earth history to the extent that they created a proverb. And it couldn’t be “ancient,” as the events it referred to were only 300 years old.
In A Time to Die this phrase is described by Picard as one of a variety of pedestrian platitudes that Vulcans were wont to utter.
Jean-Luc heard footsteps on the stone walkway just beyond his open door. He wondered if it was a visitor come to see him. A moment later, he was disappointed to see it was just another holodeck character—a wise-looking Vulcan who often stopped to dispense pedestrian platitudes and try to engage him in conversation.
The old Vulcan cleared his throat and said, “Only Nixon could go to China.”
“I’ve heard that already,” muttered Picard. “Go on your way.”
A popular use of the expression came in the 1991 film Star Trek VI: The Undiscovered Country, where "only Nixon could go to China" is quoted by Spock as "an old Vulcan proverb". In the context of the film, it is given as a reason why James T. Kirk, a character with a history of armed conflict with the Klingons and a personal enmity for them, should escort their chancellor to Earth for peace negotiations with the Federation.
It isn't a proverb, that's just Spock saying a joke, although he uses it to describe as to why Kirk would be a good choice for the mission. It's the same case as Chancellor Gorkon who knew Shakespeare wasn't written originally in Klingon.
I think JRE is seriously overthinking it.
From the very first time I saw this excellent movie my interpretation was always the same. Spock fully translates his proverbs.
There must have been some incident in Vulcan history where the more antagonistic party is the one to make peace and reached the same saying. So Spock completes the translation by filling in the names from a similar incident.
Spock's line is an ironic joke to us, but my take was that Vulcans, reasonably being well-schooled in the political histories of all the major Alpha Quadrant civilizations, found the Nixon/China story noteworthy enough to proverbialize it in their own civilization. Joshua above suggested that Spock changed the names from some Vulcan reference to Nixon and China so that the assembled humans would get the meaning; I don't find that necessary. Perhaps Vulcan history had no analogous event and so Vulcans took special note of this especially bold sociological concept, where an adversary's principal opponent is the most meaningful one to make an overture of peace because of the message of sincerity it sends.