LocaleThemeHooks.php

<?php

namespace Drupal\locale\Hook;

use Drupal\Core\Hook\Attribute\Preprocess;
use Drupal\Core\Language\LanguageInterface;
use Drupal\Core\Language\LanguageManagerInterface;

/**
 * Hook implementations for locale.
 */
class LocaleThemeHooks {
    public function __construct(LanguageManagerInterface $languageManager) {
    }
    
    /**
     * Implements hook_preprocess_HOOK() for node templates.
     */
    public function preprocessNode(&$variables) : void {
        
        /** @var \Drupal\node\NodeInterface $node */
        $node = $variables['node'];
        if ($node->language()
            ->getId() != LanguageInterface::LANGCODE_NOT_SPECIFIED) {
            $interface_language = $this->languageManager
                ->getCurrentLanguage();
            $node_language = $node->language();
            if ($node_language->getId() != $interface_language->getId()) {
                // If the node language was different from the page language, we should
                // add markup to identify the language. Otherwise the page language is
                // inherited.
                $variables['attributes']['lang'] = $node_language->getId();
                if ($node_language->getDirection() != $interface_language->getDirection()) {
                    // If text direction is different form the page's text direction, add
                    // direction information as well.
                    $variables['attributes']['dir'] = $node_language->getDirection();
                }
            }
        }
    }

}