The requested PHP extension intl is missing from your system (SonataAdminBundle) in Symfony2
Linux user
yum install php-intl
I had the same problem while I was installing new Magento 2.0, after different hit and trials, I manged to solve it by following these steps:
I copied all icu* files from php directory to Appache directory, and it worked.
Php direcotry:
WAMP\bin\php\php5.5.12
Appache Directory:
WAMP\bin\apache\apache2.4.9
Make sure to un-comment following line in php.ini file:
extension=ext/php_intl.dll
Like @Hugehornet pointed out - you should enable this extension in php.ini by uncommenting this line: extension=ext/php_intl.dll
If you use wamp's interface for this task you are actually updating the php.ini file located in apache's directory.
Example: C:\wamp\bin\apache\Apache2.4.4\bin\php.ini
Composer is using the one located in the php's installation directory.
Example: C:\wamp\bin\php\php5.4.12\php.ini
You should manually edit the latter and restart the wamp server.