I don’t know how was it originally.
But not long ago, there was transliteration filter applied. So slugs were made Korean → English weirdly.
I asked @sam to disable that feature for Korean language setting.
Also I told him that in my country, Korean slugs( ex. /t/안녕하세요-여러분-반갑습니다) are not that commonly used. We prefer just English letters and numbers like /topics/###
If Discourse slugfier accepts Korean letters exactly (Not transliteration),
I think the best way is that Admin can choose the URL types like Wordpress:
But I am not sure about Discourse slugfier mechanism, I am not an expert here, so I just report them about my opinions. 