* gnu/packages/base.scm (glibc)[arguments]: Append VERSION to
  'libc_cv_localedir'.
* gnu/system/locale.scm (localedef-command): Write to the sub-directory
  called (package-version libc) in #$output.
  (locale-directory): Create said directory.
* doc/guix.texi (Locales): Mention the per-version sub-directory.