It's my understanding that Vietnamese, though a Sino-Tibetan language, is written in the Roman alphabet (though even some languages using the Roman alphabet require specialized fonts, ie, Turkish etc.).
The language was Romanized by the Portuguese missionaries in the 1600s and effectively be the French missionaries in the 1800s and formally adopted by the emperor. As an invented written language it is highly consistent, it is pronounced as it is written. The Vietnamese are proud of their script and have the highest literacy rate in Asia. It is a tonal language and the tones are rendered by marks over the words. The old written language was written Chinese which is a separate language from the various spoken languages. The Chinese characters were rendered as "Vietnamese" by adding strokes to the Chinese ideograms. It was correspondingly more difficult to learn. Unfortunately the old literature does not work so well with the new script because it is a translation. The new script renders the spoken language. The old script was its own language with its own structure and tropes.