Recommended not to delete it, but instead just set Italian as default, and leave the english support available in case it's ever needed again.
If the tpl_languages.php sidebox is disabled in the Layout Boxes Controller, then the customers will never know English exists, and will not select it. But if you ever need it, it'll be available.
I can't speak for any of the addon contributions as to whether they require "english" specifically or not; however, most are written specifically for english sites and do not contain alternate language definitions.



