*locale-external-formats* contains the mapping from locale names to external formats that
set-locale uses to set the correct defaults for FLI. The value is an alist with elements of the form:
(locale multi-byte-ef wide-character-ef)
The locale names are given as strings. If the first character of the string is #\*, then that entry matches any locale having the rest of the string as a suffix. If the last character of the string is #\*, then that entry matches any locale having the rest of the string as a prefix. Either external format may be given as
nil, in which case the corresponding foreign type cannot be used without specifying an external format.
LispWorks Foreign Language Interface User Guide and Reference Manual - 29 Sep 2017