DateFormat.php

<?php

namespace Drupal\config_translation\FormElement;

use Drupal\Core\Language\LanguageInterface;

/**
 * Defines the date format element for the configuration translation interface.
 */
class DateFormat extends FormElementBase {
    
    /**
     * {@inheritdoc}
     */
    public function getTranslationElement(LanguageInterface $translation_language, $source_config, $translation_config) {
        
        /** @var \Drupal\Core\Datetime\DateFormatterInterface $date_formatter */
        $date_formatter = \Drupal::service('date.formatter');
        $description = $this->t('A user-defined date format. See the <a href="https://www.php.net/manual/datetime.format.php#refsect1-datetime.format-parameters">PHP manual</a> for available options.');
        $format = $this->t('Displayed as %date_format', [
            '%date_format' => $date_formatter->format(REQUEST_TIME, 'custom', $translation_config),
        ]);
        return [
            '#type' => 'textfield',
            '#description' => $description,
            '#field_suffix' => ' <small data-drupal-date-formatter="preview">' . $format . '</small>',
            '#attributes' => [
                'data-drupal-date-formatter' => 'source',
            ],
            '#attached' => [
                'drupalSettings' => [
                    'dateFormats' => $date_formatter->getSampleDateFormats($translation_language->getId()),
                ],
                'library' => [
                    'system/drupal.system.date',
                ],
            ],
        ] + parent::getTranslationElement($translation_language, $source_config, $translation_config);
    }

}