doc/dev/plugins/problems/scss/_asian.scss

// Optimized for East Asian CJK
:lang(zh),
:lang(zh-Hans) {
  font-family: $cjk-zh-hans-font-family;
}

:lang(zh-Hant) {
  font-family: $cjk-zh-hant-font-family;
}

:lang(ja) {
  font-family: $cjk-jp-font-family;
}

:lang(ko) {
  font-family: $cjk-ko-font-family;
}

:lang(zh),
:lang(ja),
.cjk {
  ins,
  u {
    border-bottom: $border-width solid;
    text-decoration: none;
  }

  del + del,
  del + s,
  ins + ins,
  ins + u,
  s + del,
  s + s,
  u + ins,
  u + u {
    margin-left: .125em;
  }
}