In https://drafts.csswg.org/css-counter-styles/ , numerous complex counting styles including a few for CJK languages have been defined. One of the counting style is korean-hangul-formal which is writing the numbers out in Korean Hangul.
However, according to the first reply in w3c/klreq#22 , there is an informal variant of the counting style that is also seen in Korean text, which omit the leading 일 for some numbers when the condition is met.
I think it would be a good idea to include the style into the specification, especially given that the complexity of the algorithm it seems like it is more suitable to add it in the css-counter-styles-3 instead of predefined-counter-styles