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.