This needs to be REQUIRED READING at the Open Group and the ISO C standards committees.

I'll quibble just a bit and say that:

  a) the C locale should be a UTF-8 locale...
     that tolerates invalid sequences (because
     the C locale historically is a just-use-8
     locale),
  
  b) even with new functions that take a locale
     handle, we need functions that use a global
     one, however that global one should be set
     once and NEVER changed in the life of the
     process, and it should be set either before
     main() starts, or before main() does anything
     that needs a locale, or starts any threads.