On XAMPP (Windows) open the php.ini by opening the control panel, selecting config on apache section and selecting PHP
Then add extension=php_intl and restart Apache
--enable-intl will enable the extension while compiling PHP.
If your ICU is installed to a non-standard directory then you might want to
specify its location in
LD_LIBRARY_PATH
environment variable so that dynamic linker can find it:
Otherwise, if PHP and ICU are installed to their default locations, then the additional options to configure are not needed.
On XAMPP (Windows) open the php.ini by opening the control panel, selecting config on apache section and selecting PHP
Then add extension=php_intl and restart Apache
For amazon nginx server (CentOs), try the following:
sudo yum install libicu-devel
sudo yum install php-intl
To install on windows uncommenting the dll in php.ini is not enough you also need to include several other libraries in your system path (not user path). Found these details here: http://stackoverflow.com/a/6086991/819883