@[M]Transliteration?
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is pretty good.
If you mean, how do you display Korean characters in ASCII, you don't, because Korean is not Latin based. It does not use the Latin Alphabet.
Korean character set (like almost all character sets) reserves the ASCII characters (32 - 128 decimal), so ASCII is
already in Korean, and Korean already complies to ASCII... what it doesn't comply to is Western European ANSI (used in Britain, France, Spain, Italy, Brazil, USA, Canada etc) or the many other popular code-pages used by users here. If we all used the same code-page, it wouldn't be a problem, but of-course people in Northern Europe have code pages for Nordic Latin accented characters, as opposed to Hispanic / Gallic Latin accented characters... Interestingly, those in Ireland (a major traditional Gaelic speaking land) require another code-page all-together, but I gather is is sufficient for Scotts Gaelic as well as Irish Gaelic.
I mention these, because they all follow basic Latin alphabet, but have different requirements for extended (accented) characters. Languages like Greek, Chinese, Japanese, Korean, Russian (and other Cyrillic based Eastern European languages) Tamil, Farsi, Gujarati, Bengali, Arabic, Hebrew etc. Don't predominantly use the Latain Alphabet at all... and yet they all still conform to the ASCII standard in the characters from 32 - 128 in their native code-page.
So A-Z and a-z plus the usual "+", "-", ",", "=", "?", "!", "$", "%" etc punctuation, is the same in any code-page... it's things like á, é, í, ó, ú, à, è, ì, ò, ù, æ, ä, ë, ï, ö, ü, ß, č, ô etc which do not travel around the world properly. They conflict with Korean characters, or Nordic, Cyrillic etc.
Don't dismiss them as "not English" either. In English the word Coupé is correctly spelled, just as I just did... if you leave the accent off, people will probably still understand you, but it's "bad English". Equally, although we typically write Æon (a term used to describe an age in the Zodiac calendar) we often write Aeon, because we can't be arsed to figure out where on our keyboard that so rarely used character is, but that's not "correct" English. The former Æon
is correct in the English language. If your English teacher at school did not correct either of these in handwritten course work, then they where remiss in their job. ^_^
I hope (but suspect otherwise) that English people know that Coupé is correctly typed "C", "o", "u", "p", AltGr+"e" on an English keyboard and a computer configured for input it international English. (I hope it still works in the U.S., but they can get sloppy)