I am getting Fatal error: Class 'IntlDateFormatter' not found in Magento2

Just need to clear comment before this line in php.ini file:

;extension=php_intl.dll

to

extension=php_intl.dll

sudo apt-get install php7.0-intl did the trick for me on Ubuntu 18.04.

(That's with this PPA repo containing a backport of PHP sudo add-apt-repository ppa:ondrej/php.)