(PHP 4, PHP 5, PHP 7, PHP 8)
textdomain — Sets the default domain
$domain): stringThis function sets the domain to search within when calls are made to gettext(), usually the named after an application.
domain
       The new message domain, or null to get the current setting without
       changing it
      
If successful, this function returns the current message domain, after possibly changing it.
Note:
The textdomain() information is maintained per process, not per thread.