PHP : "intl" extension, Windows, Apache

PHP Internationalization support ("intl") is bundled as of PHP 5.3.0 and does not require PECL:
http://www.php.net/manual/en/intl.installation.php

Things to check if it does not work under Windows/Apache:

1. php_intl.dll exists in the "ext" folder of the PHP root ( normally it's c:\Program Files\PHP\ext )
2. The php.ini file in c:\Windows folder has these lines:
   

   extension_dir="C:\Program Files\PHP\ext"
   extension=php_intl.dll

   (php.ini in c:\Program Files\PHP may work too, but I keep it in Windows folder so it's not accidentally removed when PHP is upgraded)
3. There are ICU .dll files in c:\Program Files\PHP:
   

   icudt*.dll
   icuin*.dll
   icuio*.dll
   icule*.dll
   iculx*.dll
   icutu*.dll
   icuuc*.dll

    (* is version number, for example icudt36.dll)
   
4. c:\Program Files\PHP is in the %PATH% (environment variables in Control Panel - System - Advanced - ...)
   Without that, the ICU dlls are not loaded by PHP as Apache module - no error message is displayed, but the extension is not in the phpinfo().