Class 'Locale' not found issue on CakePHP 3
Solution Xampp (Windows)
Open /xampp/php/php.ini
Change ;extension=php_intl.dll to extension=php_intl.dll (remove the semicolon)
Copy all the /xamp/php/ic*.dll files to /xampp/apache/bin
Restart apache in the Xampp control panel
Solution Linux (thanks to Annamalai Somasundaram)
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.
Restart apache sudo service apache2 restart
Solution Mac/OSX (homebrew) (thanks to deizel)
Install the php5-intl extension brew install php56-intl
If you get No available formula for php56-intl follow these instructions.
Restart apache sudo apachectl restart
Eventually you can run composer install to check if it's working.