Comment 3 for bug 475240

I am not sure about what you mean by "breaks Korean fonts". If you are looking at Han characters under en_US.UTF8 locale, you really should not expect to see Korean Hanja, because Chinese, Japanese and Korean share those code points and (simplified) Chinese Han characters are used as the default (for non-CJK locales).

If you expect to use the font variants for Korean Hanja, then please set your locale to Korean, and do fontconfig-voodoo of your locale. in this case, cjk-specific fontconfig files will be activated to show your local font variants.