In the date field, You can set the read only custom format for date display and there is a check in the presentation table to display the editable date in the read only applied format. Have your tried that.
Also, you can trying FormatDateTime function to change to particular format on change of the date field
@SARAVANAG en_EN is an invalid locale. Please try with en_US locale or any locale from the below article. This issue will be seen only when giving the invalid locales to the operators.