LanguageConverter.php

<?php

namespace Drupal\language;

use Drupal\Core\Language\LanguageManagerInterface;
use Drupal\Core\ParamConverter\ParamConverterInterface;
use Symfony\Component\Routing\Route;

/**
 * Converts parameters for upcasting entity IDs to full objects.
 */
class LanguageConverter implements ParamConverterInterface {
    
    /**
     * The language manager.
     *
     * @var \Drupal\Core\Language\LanguageManagerInterface
     */
    protected $languageManager;
    
    /**
     * Constructs a new LanguageConverter.
     *
     * @param \Drupal\Core\Language\LanguageManagerInterface $language_manager
     *   The language manager.
     */
    public function __construct(LanguageManagerInterface $language_manager) {
        $this->languageManager = $language_manager;
    }
    
    /**
     * {@inheritdoc}
     */
    public function convert($value, $definition, $name, array $defaults) {
        if (!empty($value)) {
            return $this->languageManager
                ->getLanguage($value);
        }
        return NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function applies($definition, $name, Route $route) {
        return !empty($definition['type']) && $definition['type'] == 'language';
    }

}