On the "Caveats for xterm" page it says

  On  other  operating  systems  except  OpenBSD,  there  is
  no  way  in  hell  to  make the  interaction  of  locales
  with terminal controls truly safe.

But consider a linux system based on musl libc, it's not very different from openbsd's policy of utf-8 and ascii only, it's probably pretty close even if not perfect:

http://wiki.musl-libc.org/wiki/Functional_differences_from_g...