title: Getting supported locales in browsers
body: <p>I'm using <code>date.toLocaleDateString(locale)</code> method to get the user's date format. I'm getting the user's locale on the server side with a mixture of Accept-Language header and geocoded IP address (browsers seem to default to en-US even if you are outside of the US). But toLocaleDateString() doesn't seem to recognise all locales, i.e. if you do <code>date.toLocaleDateString('en-IE')</code> you will get US date format rather than European. <code>Intl.Collator.supportedLocalesOf('en-IE', {localeMatcher: 'lookup'})</code> doesn't help. Is there a list of locales that browsers support?</p>
  
  <p>BTW I've tried the above on Chrome and Firefox on OSX.</p>