Drupal 8.0.0 beta 12. More info: https://www.drupal.org/node/2514176

core/modules/language/src/LanguageConverter.php

@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\language\LanguageConverter.
+ */
+
+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');
+  }
+
+}