Category is a named
constant (or string) specifying the category of the functions
affected by the locale setting:
LC_ALL for all of the below
LC_COLLATE for string comparison, see
strcoll()
LC_CTYPE for character classification and
conversion, for example
strtoupper()
LC_MONETARY for
localeconv()
LC_NUMERIC for decimal separator (See also
localeconv())
LC_TIME for date and time formatting with
strftime()
If locale is the empty
string "", the locale names will be
set from the values of environment variables with the same
names as the above categories, or from "LANG".
If locale is zero or
"0", the locale setting is not
affected, only the current setting is returned.
If locale is an array
or followed by additional parameters then each array element
or parameter is tried to be set as new locale until success.
This is usefull if a locale is known under different names on
different systems or for providing a fallback for a possibly
not available locale.
注: Passing multiple locales is not available before PHP 4.3.0
Setlocale returns the new current locale, or FALSE if the locale functionality is
not implemented in the platform, the specified locale does
not exist or the category name is invalid. An invalid
category name also causes a warning message.
注: The return value of setlocale() depends on the system that PHP is running. It returns exactly what the system setlocale function returns.