all, collate, ctype, messages,
monetary, numeric or time. For 
details, please consult the C library locale documentation. See also section 
2.18.1. Please note that the locale is shared between all threads 
and thread-safe usage of setlocale/3 
is in general not possible. Do locale operations before starting threads 
or thoroughly study threading aspects of locale support in your 
environment before using in multithreaded environments. Locale settings 
are used by format_time/3, collation_key/2 
and locale_sort/2.
The messages locale defines the language used by
print_message/2. 
Note that this locale is not available on all operating system. Notably 
Windows does not support this category. See
win_get_user_preferred_ui_languages/2.