The operation differs by OS.
  A Windows locale is specified like "English_United Kingdom.1252".
  The final component gives the codepage, and this defines the encoding.
  Locale names are normally like es_MX.iso88591.  If final
  component indicates an encoding and it is not utf8 we just need
  to look up the equivalent encoding name.  Otherwise, the language
  (here es) is used to choose a primary or fallback encoding.
In the C locale the answer will be "ASCII".