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Pedantic Grognard
So what? Nobody requires people to know much about the cultural history of England (or anywhere else in Europe) before they write for the Sword Coast, do they? What they've soaked up by growing up in America is fine.Yeah, but there's a difference between "Japanese person" and "Japanese person who has actually studied their culture's history."
So, as Wizards of the Coast, you contract with, say, Group SNE (located in Japan, owned and staffed by Japanese people, creators of both of original RPGs and of Japanese translations of English ones) to do a version of Kozakura and Wa that is actually gameable, rather than being (like the Kara-Tur boxed set) a regurgitated history book plus D&D game references.
Off the top of my head I don't know a Chinese or Korean company to contract with, but I'm sure Taiwan has people who could be hired to revise Shou Lung and T'u Lung, and there's South Koreans who could provide a revised Koryo.