Reset locale specific date formats to the global defaults.
$langcode: Language code, e.g. 'en'.
function locale_date_format_reset_form($form, &$form_state, $langcode) {
$form['langcode'] = array(
'#type' => 'value',
'#value' => $langcode,
);
$languages = language_list();
return confirm_form($form, t('Are you sure you want to reset the date formats for %language to the global defaults?', array(
'%language' => $languages[$langcode]->name,
)), 'admin/config/regional/date-time/locale', t('Resetting will remove all localized date formats for this language. This action cannot be undone.'), t('Reset'), t('Cancel'));
}