I’ve lived in Madison, a city with a really big Hmong community, for more than a decade, and I only just now learned something kinda basic about the most common transliteration system for the Hmong language.
Hmong, like Chinese, is tonal. When you write Chinese in pinyin, you draw a tone mark over each syllable to indicate tone; like mā (‘mother’) or mǎ (‘horse.’)
In Hmong, the tone is indicated by an extra character placed at the end of the syllable. The character looks like a Roman consonant, but it’s not — it’s a tone mark. So “Hmoob,” which is the Hmong word for the Hmong language isn’t pronounced to rhyme with “tube” — the syllable ends with a nasalized vowel, and the character “b” is just there to tell you to pronounce the word in a high tone. “Hmoov” (“flour”) differs from “Hmoob” only in tone.
This was also the way that Gwoyeu Romatzyh (国语罗马字, https://en.wikipedia.org/wiki/Gwoyeu_Romatzyh) handled transliteration of tones in Chinese. However unlike Hmong, the orthographic changes for different tones weren’t uniform (!!) across different types of syllables (perhaps why GR fell out of favor). For example, here are some different sounds and their GR transcriptions in 1st tone, 2nd tone, 3rd tone, and 4th tone:
1st 2nd 3rd 4th
shiue shyue sheue shiueh
chuan chwan choan chuann
chang charng chaang changq
hai hair hae hay
bau baur bao baw
mha ma maa mah
(pinyin: xue, chuan, chang, hai, bao, ma)
That explains how my friend Theresa Chiueh’s name is spelled!
Chern and Terng are also notable examples in Chinese, where the r was originally meant to be a silent tone indicator. Noone seems to talk about Chen classes, though.