Vietnamese is written in Latin letters because of a 17th-century missionary's notebook

Vietnamese had been written in Chinese-derived characters for centuries, but Portuguese Jesuit missionary Francisco de Pina devised a Latin-based romanization in the early 1600s to help fellow missionaries learn the language's tones. Alexandre de Rhodes built on that work and published it in a 1651 Vietnamese-Portuguese-Latin dictionary. That script, Quoc Ngu, eventually replaced Chinese characters entirely and is now Vietnam's official writing system.

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