I don't know how to read Korean yet, but assuming you can fit all the hangul characters you need into the same space as the Japanese/English font, you should have no problems. You'll just need to create a table.

Use my program, TheCheat. You can get it from my website, or from here at RHDN. Just look under "Utilities".

Copy the font you're going to use to a bitmap image, import the table and you can configure TheCheat to simulate an in-game text box. ^_^

Are you talking about physically changing the in-game text/hex encoding of letters from 2bytes to 1byte within the rom to save on space and allow you to fit more expanded text?

e.g. table structure:  0A1C=A   to like  0A=A ?

just curious...