Bug in datetime regional settings: 'en' is missing !!!
Why regional ['it'] is here, but ['en'] not ? there are some ['en-<some thing>'] but not a base 'en'.
So from PHP i cannot use en or it AND i cannot user en-US and it-IT and it-CH ...
why ?!?!
It's a big inconsistence (imho)
... and sorry for my bad english
see the file jquery-ui-i18n.js