LanguageBlock.php

<?php

namespace Drupal\language\Plugin\Derivative;

use Drupal\Component\Plugin\Derivative\DeriverBase;
use Drupal\Core\StringTranslation\StringTranslationTrait;
use Drupal\language\ConfigurableLanguageManagerInterface;

/**
 * Provides language switcher block plugin definitions for all languages.
 */
class LanguageBlock extends DeriverBase {
    use StringTranslationTrait;
    
    /**
     * {@inheritdoc}
     */
    public function getDerivativeDefinitions($base_plugin_definition) {
        $language_manager = \Drupal::languageManager();
        if ($language_manager instanceof ConfigurableLanguageManagerInterface) {
            $info = $language_manager->getDefinedLanguageTypesInfo();
            $configurable_types = $language_manager->getLanguageTypes();
            foreach ($configurable_types as $type) {
                $this->derivatives[$type] = $base_plugin_definition;
                $this->derivatives[$type]['admin_label'] = $this->t('Language switcher (@type)', [
                    '@type' => $info[$type]['name'],
                ]);
            }
            // If there is just one configurable type then change the title of the
            // block.
            if (count($configurable_types) == 1) {
                $this->derivatives[reset($configurable_types)]['admin_label'] = $this->t('Language switcher');
            }
        }
        return parent::getDerivativeDefinitions($base_plugin_definition);
    }

}