This form is used to create or edit a locale for your site.

• Locale: The first two letters should be a ISO 639 code. The last two letters should be a ISO 3166 country code.
• Enabled: check to enable the locale for users of the site.
• Name: name of the locale for easy identification.
• Date format: format to use when displaying the date.
• Long date format: format to use when displaying a long version of the date.
• Extended date format: format to use when displaying an extended version of the date.
• Input date format: format of date used in input fields.
• Time format: format to use when displaying time.
• Short time format: format to use when displaying a short version of the time.
• Input time format: format of time used in input fields.
• Start of the week: select the first day of the week.
• Lang file: the folder that contains the language files under the locales sub-directory
• Priority: priority of the locale when selecting a locale from a language code.

More details on date/time format strings can be found here