From a purely technical perspective, locales and cultures have no bearing on timezones (i.e., en-US does not mean or even imply the EST time zone, or any other time zone). This is not a Sitecore specific detail.

Inside the _CMS_, dates are _displayed_ and take _input_ based on the [ServerTimeZone][1] setting. However, all dates are _stored_ inside the database as UTC and retrieved as UTC. 

The language version of an item has no bearing on what time zone the date/time field is using for input. If you want the ability to set specific time zones on date fields, you'll need to use a custom field such as this one: [CustomDateTimeZone][2] 


  [1]: https://doc.sitecore.net/sitecore_experience_platform/setting_up_and_maintaining/utc/settings_supporting_utc_implementation
  [2]: https://github.com/mikaelnet/Sitecore.DateTimeZoneField/blob/master/CustomDateTimeZone.cs