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

core/modules/language/src/LanguageSwitcherInterface.php

@@ -0,0 +1,33 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\language\LanguageSwitcherInterface.
+ */
+
+namespace Drupal\language;
+
+use Drupal\Core\Url;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Interface for language switcher classes.
+ */
+interface LanguageSwitcherInterface {
+
+  /**
+   * Returns language switch links.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The current request.
+   * @param string $type
+   *   The language type.
+   * @param \Drupal\Core\Url $url
+   *   The URL the switch links will be relative to.
+   *
+   * @return array
+   *   An array of link arrays keyed by language code.
+   */
+  public function getLanguageSwitchLinks(Request $request, $type, Url $url);
+
+}