[mc32]

Vietnam adopted the Latin alphabet from a missionary of some sort a couple of centuries before they were colonized by France --at the time Vietnam was decolonizing from China. The French made some modifications to how the alphabet was used to represent their phonemes.

[dboreham]

Btw, after a couple of days being super-confused in Thailand I reverse-engineered this history from signs in English I kept seeing that in no way matched the Thai pronunciation. Finally the penny dropped that whoever had come up with the "English" phonetic spelling of Thai words, was not an English speaker.