Mule doesn’t have a Unicode charset internally, so there’s nothing to bind a Unicode registry to. It would not be straightforward to create, either, because Unicode is not ISO 2022-compatible. You’d have to translate it to multiple 96x96 pages.
This means that Mule-UCS uses ordinary national fonts for display. This is not really a problem, except for those languages that use the Unified Han characters. The problem here is that Mule-UCS maps from Unicode code points to national character sets in a deterministic way. By default, this means that Japanese fonts are tried first, then Chinese, then Korean. To change the priority ordering, use the command ‘un-define-change-charset-order’.
It also means you can’t use Unicode fonts directly, at least not without extreme hackery. You can run -nw with (set-terminal-coding-system ’utf-8) if you really want a Unicode font for some reason.
Real Unicode support will be introduced in SXEmacs 22.2.