Updated: 16/10/2012 12:26pm
As per 12-08-2012 a patch is merged into version 3.0 for the implementation of the the jQuery UI DatePicker in the DateField. Some jQuery locale files were adapted to mirror the Zend_date locale values, thus allowing for the use of (short) day and month names in the date format, even on different locales. If the locale file for the current language does not exist, the DatePicker will use a default 'numeric' date format, so the input will validate. Ater saving the date the requested format will be correctly displayed.
Find the documentation for the DateField here
In languages other then en_US, (short) day and monthnames could not be used in the DateFormat: the jQuery DatePicker would revert to the en_US values, since it had no locale files of its own. The DateField would then use Zend Date to validate that input and that validation would fail. You couldn't just add the existing jQuery UI locale files, since the values in those files would often be different from what Zend Date was using, so that wouldn't help much.
So that needed two actions: