LanguageNegotiationUser.php

<?php

namespace Drupal\user\Plugin\LanguageNegotiation;

use Drupal\Core\StringTranslation\TranslatableMarkup;
use Drupal\language\Attribute\LanguageNegotiation;
use Drupal\language\LanguageNegotiationMethodBase;
use Symfony\Component\HttpFoundation\Request;

/**
 * Class for identifying language from the user preferences.
 */
class LanguageNegotiationUser extends LanguageNegotiationMethodBase {
    
    /**
     * The language negotiation method id.
     */
    const METHOD_ID = 'language-user';
    
    /**
     * {@inheritdoc}
     */
    public function getLangcode(?Request $request = NULL) {
        $langcode = NULL;
        // User preference (only for authenticated users).
        if ($this->languageManager && $this->currentUser
            ->isAuthenticated()) {
            $preferred_langcode = $this->currentUser
                ->getPreferredLangcode(FALSE);
            $languages = $this->languageManager
                ->getLanguages();
            if (!empty($preferred_langcode) && isset($languages[$preferred_langcode])) {
                $langcode = $preferred_langcode;
            }
        }
        // No language preference from the user.
        return $langcode;
    }

}