It's interesting how different languages treat the same sounds. I'm thinking today about diphthongs that English treats as single vowel sounds but are very clearly two separate vowels when written in Hangul...
The Long A (as in 'lake') is actually "eh-ee" and is obvious when written in Korean (에이) or Japanese (えい), both transliterated as "ei".
The Long I (as in 'like') is actually "ah-ee" and is obvious when written in Korean (아이) or Japanese (あい), both transliterated as "ai".
The ou/au/ow as in 'house' is actually "ah-oo" and is obvious when written in Korean (아우) or Japanese (あう), both transliterated as "au", though I don't know if it's used in Japan. So the Koreans would transliterate "wow" as 와우 which returns as wau.
An interesting one is the Long O (as in 'goat') that I don't yet get exactly... In Korean it's 오우 "o-oo". I wanna say it's a Short O (as in 'box') followed by the Long OO (as in 'school'). I usually pronounce 오 as the Long O, so that's not helping me.
Last is the oi/oy (as in 'boy'). The Koreans translate it as 오이, but they always pronounce it as two distinct vowels. So, they frequently pronounce "joy" as "joey"...
It's good to remember this if you ever try to teach the kids how to rhyme in English. Like, I'll ask for rhymes of "right" (라잇), but the kids will want to add "eat" (잇)... Sure, that makes sense in Korean, but they're two very different vowels to us native English speakers.