da questo link ho trovato :

http://ejflavors.com/php/ref.gettext.html

Installation
To include GNU gettext support in your PHP build you must add the option --with-gettext[=DIR] where DIR is the gettext install directory, defaults to /usr/local.

Note to Win32 Users: In order to enable this module on a Windows environment, you must copy gnu_gettext.dll from the DLL folder of the PHP/Win32 binary package to the SYSTEM32 folder of your windows machine. (Ex: C:\WINNT\SYSTEM32 or C:\WINDOWS\SYSTEM32). Starting with PHP 4.2.3 the name changed to libintl-1.dll, this requires also iconv.dll to be copied.