You are so German. Truyen Kieu is the story of Vuong Thuy Kieu, who lived in Ming China, not in Vietnam.
"Rằng năm Gia Tĩnh triều Minh,
Bốn phương phẳng lặng, hai kinh vững vàng (the two capitals mentioned here were Changan and Louyang) (Trường An và Lạc Dương)
However, it was written in Nom script, not in Hanji. Although Nom script originated from Hanji, it is still different because it can record pure Vietnamese words
From wiki
Nguyễn Du made use of the plot of a seventeenth-century Chinese novel,
Jīn Yún Qiào (
Chinese: 金雲翹), known in Vietnamese pronunciation of Chinese characters as
Kim Vân Kiều. The original, written by an otherwise unknown writer under the pseudonym
Qīngxīn Cáirén (
Chinese: 青心才人 "Pure-Hearted Man of Talent"), was a straightforward romance, but Nguyễn Du chose it to convey the social and political upheavals at the end of the 18th century in Vietnam.
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