Things to check if it does not work under Windows/Apache:
- php_intl.dll exists in the "ext" folder of the PHP root ( normally it's c:\Program Files\PHP\ext )
- The php.ini file in c:\Windows folder has these lines:
extension_dir="C:\Program Files\PHP\ext"(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)
- There are ICU .dll files in c:\Program Files\PHP:
icudt*.dll(* is version number, for example icudt36.dll)
- 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().