CakePHP 3.0 installation: intl extension missing from system

I faced the same problem today. You need to enable the intl PHP extension in your PHP configuration (.ini).

Solution Xampp (Windows)

1. Open /xampp/php/php.ini
2. Change ;extension=php_intl.dll to extension=php_intl.dll (remove the semicolon)
3. Copy all the /xampp/php/ic*.dll files to /xampp/apache/bin
4. Restart apache in the Xampp control panel

Solution Linux (thanks to Annamalai Somasundaram)

1. Install the php5-intl extension sudo apt-get install php5-intl

   1.1. Alternatively use sudo yum install php5-intl if you are on CentOS or Fedora.

2. Restart apache sudo service apache2 restart

Solution Mac/OSX (homebrew) (thanks to deizel)

1. Install the php5-intl extension brew install php56-intl
2. If you get No available formula for php56-intl follow these instructions.
3. Restart apache sudo apachectl restart

Eventually you can run composer install to check if it’s working. It will give an error if it’s not.