class LanguageFormatter

class LanguageFormatter extends StringFormatter {
    
    /**
     * The language manager.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * Constructs a LanguageFormatter instance.
     *
     * @param string $plugin_id
     *   The plugin ID for the formatter.
     * @param mixed $plugin_definition
     *   The plugin implementation definition.
     * @param \Drupal\Core\Field\FieldDefinitionInterface $field_definition
     *   The definition of the field to which the formatter is associated.
     * @param array $settings
     *   The formatter settings.
     * @param string $label
     *   The formatter label display setting.
     * @param string $view_mode
     *   The view mode.
     * @param array $third_party_settings
     *   Any third party settings.
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager.
     * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
     *   The language manager.
     */
    public function __construct($plugin_id, $plugin_definition, FieldDefinitionInterface $field_definition, array $settings, $label, $view_mode, array $third_party_settings, EntityTypeManagerInterface $entity_type_manager, LanguageManagerInterface $language_manager) {
        parent::__construct($plugin_id, $plugin_definition, $field_definition, $settings, $label, $view_mode, $third_party_settings, $entity_type_manager);
        $this->languageManager = $language_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
        return new static($plugin_id, $plugin_definition, $configuration['field_definition'], $configuration['settings'], $configuration['label'], $configuration['view_mode'], $configuration['third_party_settings'], $container->get('entity_type.manager'), $container->get('language_manager'));
    }
    
    /**
     * {@inheritdoc}
     */
    public static function defaultSettings() {
        $settings = parent::defaultSettings();
        $settings['native_language'] = FALSE;
        return $settings;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsForm(array $form, FormStateInterface $form_state) {
        $form = parent::settingsForm($form, $form_state);
        $form['native_language'] = [
            '#title' => $this->t('Display in native language'),
            '#type' => 'checkbox',
            '#default_value' => $this->getSetting('native_language'),
        ];
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function settingsSummary() {
        $summary = parent::settingsSummary();
        if ($this->getSetting('native_language')) {
            $summary[] = $this->t('Displayed in native language');
        }
        return $summary;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function viewValue(FieldItemInterface $item) {
        // The 'languages' cache context is not necessary because the language is
        // either displayed in its configured form (loaded directly from config
        // storage by LanguageManager::getLanguages()) or in its native language
        // name. That only depends on formatter settings and no language condition.
        $languages = $this->getSetting('native_language') ? $this->languageManager
            ->getNativeLanguages(LanguageInterface::STATE_ALL) : $this->languageManager
            ->getLanguages(LanguageInterface::STATE_ALL);
        // \Drupal\Core\Language\LanguageInterface::LANGCODE_NOT_SPECIFIED
        // and \Drupal\Core\Language\LanguageInterface::LANGCODE_NOT_APPLICABLE are
        // not returned from the language manager above.
        $value = [];
        if (isset($item->language)) {
            $name = isset($languages[$item->language
                ->getId()]) ? $languages[$item->language
                ->getId()]
                ->getName() : $item->language
                ->getId();
            $value = [
                '#plain_text' => $name,
            ];
        }
        return $value;
    }

}