diff --git a/core/includes/menu.inc b/core/includes/menu.inc
index ddbaca2..80be82d 100644
--- a/core/includes/menu.inc
+++ b/core/includes/menu.inc
@@ -5,19 +5,12 @@
  * API for the Drupal menu system.
  */
 
-use Drupal\Component\Utility\NestedArray;
 use Drupal\Component\Utility\String;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Language\Language;
-use Drupal\Core\ParamConverter\ParamNotConvertedException;
-use Drupal\Core\Routing\RequestHelper;
 use Drupal\Core\Template\Attribute;
-use Drupal\menu_link\Entity\MenuLink;
 use Drupal\menu_link\MenuLinkInterface;
-use Drupal\menu_link\MenuLinkStorageController;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
-use Symfony\Component\HttpFoundation\Request;
-use Symfony\Component\Routing\Route;
 
 /**
  * @defgroup menu Menu and routing system
@@ -312,55 +305,6 @@
 const MENU_PREFERRED_LINK = '1cf698d64d1aa4b83907cf6ed55db3a7f8e92c91';
 
 /**
- * Unserializes menu data, using a map to replace path elements.
- *
- * The menu system stores various path-related information (such as the 'page
- * arguments' and 'access arguments' components of a menu item) in the database
- * using serialized arrays, where integer values in the arrays represent
- * arguments to be replaced by values from the path. This function first
- * unserializes such menu information arrays, and then does the path
- * replacement.
- *
- * The path replacement acts on each integer-valued element of the unserialized
- * menu data array ($data) using a map array ($map, which is typically an array
- * of path arguments) as a list of replacements. For instance, if there is an
- * element of $data whose value is the number 2, then it is replaced in $data
- * with $map[2]; non-integer values in $data are left alone.
- *
- * As an example, an unserialized $data array with elements ('node_load', 1)
- * represents instructions for calling the node_load() function. Specifically,
- * this instruction says to use the path component at index 1 as the input
- * parameter to node_load(). If the path is 'node/123', then $map will be the
- * array ('node', 123), and the returned array from this function will have
- * elements ('node_load', 123), since $map[1] is 123. This return value will
- * indicate specifically that node_load(123) is to be called to load the node
- * whose ID is 123 for this menu item.
- *
- * @param $data
- *   A serialized array of menu data, as read from the database.
- * @param $map
- *   A path argument array, used to replace integer values in $data; an integer
- *   value N in $data will be replaced by value $map[N]. Typically, the $map
- *   array is generated from a call to the arg() function.
- *
- * @return
- *   The unserialized $data array, with path arguments replaced.
- */
-function menu_unserialize($data, $map) {
-  if ($data = unserialize($data)) {
-    foreach ($data as $k => $v) {
-      if (is_int($v)) {
-        $data[$k] = isset($map[$v]) ? $map[$v] : '';
-      }
-    }
-    return $data;
-  }
-  else {
-    return array();
-  }
-}
-
-/**
  * Localizes the router item title using t() or another callback.
  *
  * Translate the title and description to allow storage of English title
@@ -369,29 +313,12 @@ function menu_unserialize($data, $map) {
  *
  * @param $item
  *   A menu router item or a menu link item.
- * @param $map
- *   The path as an array with objects already replaced. E.g., for path
- *   node/123 $map would be array('node', $node) where $node is the node
- *   object for node 123.
  * @param $link_translate
  *   TRUE if we are translating a menu link item; FALSE if we are
  *   translating a menu router item.
- *
- * @return
- *   No return value.
- *   $item['title'] is localized according to $item['title_callback'].
- *   If an item's callback is check_plain(), $item['options']['html'] becomes
- *   TRUE.
- *   $item['description'] is computed using $item['description_callback'] if
- *   specified; otherwise it is translated using t().
- *   When doing link translation and the $item['options']['attributes']['title']
- *   (link title attribute) matches the description, it is translated as well.
  */
-function _menu_item_localize(&$item, $map, $link_translate = FALSE) {
+function _menu_item_localize(&$item, $link_translate = FALSE) {
   // Allow default menu links to be translated.
-  // @todo Figure out a proper way to support translations of menu links, see
-  //   https://drupal.org/node/2193777.
-  $title_callback = $item instanceof MenuLinkInterface && !$item->customized ? 't' :  $item['title_callback'];
   $item['localized_options'] = $item['options'];
   // All 'class' attributes are assumed to be an array during rendering, but
   // links stored in the database may use an old string value.
@@ -412,104 +339,18 @@ function _menu_item_localize(&$item, $map, $link_translate = FALSE) {
     // we handle it directly instead of using indirect, slower methods.
     // @todo Recheck this line once https://drupal.org/node/2084421 is in.
     $item['title'] = isset($item['link_title']) ? $item['link_title'] : $item['title'];
-    if ($title_callback == 't') {
-      if (empty($item['title_arguments'])) {
-        $item['title'] = t($item['title']);
-      }
-      else {
-        $item['title'] = t($item['title'], menu_unserialize($item['title_arguments'], $map));
-      }
-    }
-    elseif ($title_callback) {
-      if (empty($item['title_arguments'])) {
-        $item['title'] = $title_callback($item['title']);
-      }
-      else {
-        $item['title'] = call_user_func_array($title_callback, menu_unserialize($item['title_arguments'], $map));
-      }
-      // Avoid calling check_plain again on l() function.
-      if ($title_callback == 'check_plain') {
-        $item['localized_options']['html'] = TRUE;
-      }
-    }
+    // @todo Figure out a proper way to support translations of menu links, see
+    //   https://drupal.org/node/2193777.
+    $item['title'] = t($item['title']);
   }
   elseif ($link_translate) {
     $item['title'] = $item['link_title'];
   }
-
-  // Translate description, see the motivation above.
-  if (!empty($item['description'])) {
-    $original_description = $item['description'];
-  }
-  if (!empty($item['description_arguments']) || !empty($item['description'])) {
-    $description_callback = $item['description_callback'];
-    // If the description callback is t(), call it directly.
-    if ($description_callback == 't') {
-      if (empty($item['description_arguments'])) {
-        $item['description'] = t($item['description']);
-      }
-      else {
-        $item['description'] = t($item['description'], menu_unserialize($item['description_arguments'], $map));
-      }
-    }
-    elseif ($description_callback) {
-      // If there are no arguments, call the description callback directly.
-      if (empty($item['description_arguments'])) {
-        $item['description'] = $description_callback($item['description']);
-      }
-      // Otherwise, use call_user_func_array() to pass the arguments.
-      else {
-        $item['description'] = call_user_func_array($description_callback, menu_unserialize($item['description_arguments'], $map));
-      }
-    }
-  }
-  // If the title and description are the same, use the translated description
-  // as a localized title.
-  if ($link_translate && isset($original_description) && isset($item['options']['attributes']['title']) && $item['options']['attributes']['title'] == $original_description) {
-    $item['localized_options']['attributes']['title'] = $item['description'];
-  }
-}
-
-/**
- * Handles dynamic path translation and menu access control.
- *
- * When a user arrives on a page such as node/5, this function determines
- * what "5" corresponds to, by inspecting the page's menu path definition,
- * node/%node. This will call node_load(5) to load the corresponding node
- * object.
- *
- * It also works in reverse, to allow the display of tabs and menu items which
- * contain these dynamic arguments, translating node/%node to node/5.
- *
- * Translation of menu item titles and descriptions are done here to
- * allow for storage of English strings in the database, and translation
- * to the language required to generate the current page.
- *
- * @param $router_item
- *   A menu router item
- * @param string
- *   The path.
- */
-function _menu_translate(&$router_item, $path) {
-  // Generate the link path for the page request or local tasks.
-  $route = \Drupal::service('router.route_provider')->getRouteByName($router_item['route_name']);
-  $request = RequestHelper::duplicate(\Drupal::request(), '/' . $path);
-  $request->attributes->set('_system_path', $path);
-  $router_item['access'] = menu_item_route_access($route, $request);
-
-  // For performance, don't localize an item the user can't access.
-  if ($router_item['access']) {
-    $map = explode('/', $path);
-    _menu_item_localize($router_item, $map);
-  }
 }
 
 /**
  * Provides menu link unserializing, access control, and argument handling.
  *
- * This function is similar to _menu_translate(), but it also does
- * link-specific preparation.
- *
  * @param array $item
  *   The passed in item has the following keys:
  *   - access: (optional) Becomes TRUE if the item is accessible, FALSE
@@ -549,7 +390,7 @@ function _menu_link_translate(&$item) {
     }
     // For performance, don't localize a link the user can't access.
     if ($item['access']) {
-      _menu_item_localize($item, array(), TRUE);
+      _menu_item_localize($item, TRUE);
     }
   }
 
@@ -562,32 +403,6 @@ function _menu_link_translate(&$item) {
 }
 
 /**
- * Checks access to a menu item by mocking a request for a path.
- *
- * @param \Symfony\Component\Routing\Route $route
- *   Router for the given menu item.
- * @param \Symfony\Component\HttpFoundation\Request $request
- *   The current request object, used to find the current route.
- *
- * @return bool
- *   TRUE if the user has access or FALSE if the user should be presented
- *   with access denied.
- *
- */
-function menu_item_route_access(Route $route, Request $request) {
-  // Attempt to match this path to provide a fully built request to the
-  // access checker.
-  try {
-    $request->attributes->add(\Drupal::service('router')->matchRequest($request));
-  }
-  catch (ParamNotConvertedException $e) {
-    return FALSE;
-  }
-
-  return \Drupal::service('access_manager')->check($route, $request, \Drupal::currentUser());
-}
-
-/**
  * Renders a menu tree based on the current path.
  *
  * @param $menu_name
@@ -1757,8 +1572,9 @@ function menu_link_get_preferred($path = NULL, $selected_menu = NULL) {
         foreach ($menu_names as $menu_name) {
           if (empty($preferred_links[$path][$menu_name]) && isset($candidates[$link_path][$menu_name])) {
             $candidate_item = $candidates[$link_path][$menu_name];
-            _menu_translate($candidate_item, $path);
+            $candidate_item['access'] = \Drupal::service('access_manager')->checkNamedRoute($candidate_item['route_name'], $candidate_item['route_parameters'], \Drupal::currentUser());
             if ($candidate_item['access']) {
+              _menu_item_localize($candidate_item);
               $preferred_links[$path][$menu_name] = $candidate_item;
               if (empty($preferred_links[$path][MENU_PREFERRED_LINK])) {
                 // Store the most specific link.
diff --git a/core/includes/path.inc b/core/includes/path.inc
index ef169f4..3193d0e 100644
--- a/core/includes/path.inc
+++ b/core/includes/path.inc
@@ -5,8 +5,9 @@
  * Functions to handle paths in Drupal.
  */
 
+use Drupal\Component\Utility\Url;
+use Drupal\Core\ParamConverter\ParamNotConvertedException;
 use Drupal\Core\Routing\RequestHelper;
-use Symfony\Component\HttpFoundation\Request;
 
 /**
  * Check if the current page is the front page.
@@ -191,22 +192,34 @@ function path_get_admin_paths() {
  *   FALSE otherwise.
  */
 function drupal_valid_path($path) {
-  $is_valid = FALSE;
   // External URLs and the front page are always valid.
-  if ($path == '<front>' || url_is_external($path)) {
-    $is_valid = TRUE;
+  if ($path == '<front>' || Url::isExternal($path)) {
+    return TRUE;
   }
 
   // Check the routing system.
-  elseif (($collection = \Drupal::service('router.route_provider')->getRoutesByPattern('/' . $path)) && $collection->count() > 0) {
-    $routes = $collection->all();
-    $route = reset($routes);
-    $request = RequestHelper::duplicate(\Drupal::request(), '/' . $path);
-    $request->attributes->set('_system_path', $path);
-
-    // We indicate that a menu administrator is running the menu access check.
-    $request->attributes->set('_menu_admin', TRUE);
-    $is_valid = menu_item_route_access($route, $request);
+  $collection = \Drupal::service('router.route_provider')->getRoutesByPattern('/' . $path);
+  if ($collection->count() == 0) {
+    return FALSE;
   }
-  return $is_valid;
+
+  $request = RequestHelper::duplicate(\Drupal::request(), '/' . $path);
+  $request->attributes->set('_system_path', $path);
+
+  // We indicate that a menu administrator is running the menu access check.
+  $request->attributes->set('_menu_admin', TRUE);
+
+  // Attempt to match this path to provide a fully built request to the
+  // access checker.
+  try {
+    $request->attributes->add(\Drupal::service('router')->matchRequest($request));
+  }
+  catch (ParamNotConvertedException $e) {
+    return FALSE;
+  }
+
+  // Consult the accsss manager.
+  $routes = $collection->all();
+  $route = reset($routes);
+  return \Drupal::service('access_manager')->check($route, $request, \Drupal::currentUser());
 }
diff --git a/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php b/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
index 476d006..72fe06a 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
@@ -112,6 +112,15 @@ protected function doTestTitleMenuCallback() {
   }
 
   /**
+   * Tests menu item descriptions.
+   */
+  protected function doTestDescriptionMenuItems() {
+    // Verify that the menu router item title is output as page title.
+    $this->drupalGet('menu_callback_description');
+    $this->assertText(t('Menu item description text'));
+  }
+
+  /**
    * Tests for menu_link_maintain().
    */
   protected function doTestMenuLinkMaintain() {
diff --git a/core/modules/system/lib/Drupal/system/Tests/Routing/RouterPermissionTest.php b/core/modules/system/lib/Drupal/system/Tests/Routing/RouterPermissionTest.php
index d70bb18..e33156d 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Routing/RouterPermissionTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Routing/RouterPermissionTest.php
@@ -38,19 +38,6 @@ public function testPermissionAccess() {
     $path = 'router_test/test7';
     $this->drupalGet($path);
     $this->assertResponse(403, "Access denied for a route where we don't have a permission");
-    // An invalid path should throw an exception.
-    $path .= 'invalid';
-    $request = RequestHelper::duplicate(\Drupal::request(), '/' . $path);
-    $request->attributes->set('_system_path', $path);
-    $route = \Drupal::service('router.route_provider')->getRouteByName('router_test.7');
-    try {
-      menu_item_route_access($route, $request);
-      $exception = FALSE;
-    }
-    catch (ResourceNotFoundException $e) {
-      $exception = TRUE;
-    }
-    $this->assertTrue($exception, 'A ResourceNotFoundException was thrown while checking access for an invalid route.');
 
     $this->drupalGet('router_test/test8');
     $this->assertResponse(403, 'Access denied by default if no access specified');
diff --git a/core/modules/system/tests/modules/menu_test/menu_test.module b/core/modules/system/tests/modules/menu_test/menu_test.module
index d718848..08e6382 100644
--- a/core/modules/system/tests/modules/menu_test/menu_test.module
+++ b/core/modules/system/tests/modules/menu_test/menu_test.module
@@ -17,6 +17,20 @@ function menu_test_menu_link_defaults() {
     'route_name' => 'menu_test.menu_name_test',
     'menu_name' => menu_test_menu_name(),
   );
+  // This item uses SystemController::systemAdminMenuBlockPage() to list child
+  // items.
+  $items['menu_test.menu_callback_description'] = array(
+    'link_title' => 'Menu item title',
+    'description' => 'Menu item description parent',
+    'route_name' => 'menu_test.callback_description',
+  );
+  // This item tests the description key.
+  $items['menu_test.menu_callback_description.description-plain'] = array(
+    'link_title' => 'Menu item with a regular description',
+    'description' => 'Menu item description text',
+    'route_name' => 'menu_test.callback_description_plain',
+    'parent' => 'menu_test.menu_callback_description',
+  );
 
   $items['menu_test.menu_no_title_callback'] = array(
     'link_title' => 'A title with @placeholder',
diff --git a/core/modules/system/tests/modules/menu_test/menu_test.routing.yml b/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
index 9680e0f..34d5dad 100644
--- a/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
+++ b/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
@@ -21,6 +21,21 @@ menu_test.login_callback:
   requirements:
     _access: 'TRUE'
 
+menu_test.callback_description:
+  path: '/menu_callback_description'
+  defaults:
+    _content: '\Drupal\system\Controller\SystemController::systemAdminMenuBlockPage'
+  requirements:
+    _access: 'TRUE'
+
+menu_test.callback_description_plain:
+  path: '/menu_callback_description/description-plain'
+  defaults:
+    _title: 'Menu item with a regular description'
+    _content: '\Drupal\menu_test\Controller\MenuTestController::menuTestCallback'
+  requirements:
+    _access: 'TRUE'
+
 menu_test.menu_no_title_callback:
   path: '/menu_no_title_callback'
   defaults: