diff --git a/core/core.services.yml b/core/core.services.yml
index afccb31..1fb5f8b 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -1117,6 +1117,11 @@ services:
     arguments: ['@unrouted_url_assembler', '@router.request_context']
     tags:
       - { name: event_subscriber }
+  route_normalizer_request_subscriber:
+    class: Drupal\Core\EventSubscriber\RouteNormalizerRequestSubscriber
+    arguments: ['@url_generator', '@path.matcher']
+    tags:
+      - { name: event_subscriber }
   redirect_leading_slashes_subscriber:
     class: Drupal\Core\EventSubscriber\RedirectLeadingSlashesSubscriber
     tags:
diff --git a/core/lib/Drupal/Core/EventSubscriber/RouteNormalizerRequestSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/RouteNormalizerRequestSubscriber.php
new file mode 100644
index 0000000..14dce75
--- /dev/null
+++ b/core/lib/Drupal/Core/EventSubscriber/RouteNormalizerRequestSubscriber.php
@@ -0,0 +1,123 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Core\EventSubscriber\RouteNormalizerRequestSubscriber.
+ */
+
+namespace Drupal\Core\EventSubscriber;
+
+use Drupal\Core\Path\PathMatcherInterface;
+use Drupal\Core\Routing\UrlGeneratorInterface;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpKernel\KernelEvents;
+use Symfony\Component\HttpKernel\Event\GetResponseEvent;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\HttpFoundation\RedirectResponse;
+
+/**
+ * Sets the $request property on the language manager.
+ */
+class RouteNormalizerRequestSubscriber implements EventSubscriberInterface {
+
+  /**
+   * The URL generator service.
+   *
+   * @var \Drupal\Core\Routing\UrlGeneratorInterface
+   */
+  protected $urlGenerator;
+
+  /**
+   * The path matcher service.
+   *
+   * @var \Drupal\Core\Path\PathMatcherInterface
+   */
+  protected $pathMatcher;
+
+  /**
+   * The request object created by Request::createFromGlobals().
+   *
+   * @var \Symfony\Component\HttpFoundation\Request
+   */
+  protected $requestFromGlobals;
+
+  /**
+   * Constructs a RouteNormalizerRequestSubscriber object.
+   *
+   * @param \Drupal\Core\Routing\UrlGeneratorInterface $url_generator
+   *   The URL generator service.
+   * @param \Drupal\Core\Path\PathMatcherInterface $path_matcher
+   *   The path matcher service.
+   */
+  public function __construct(UrlGeneratorInterface $url_generator, PathMatcherInterface $path_matcher) {
+    $this->urlGenerator = $url_generator;
+    $this->pathMatcher = $path_matcher;
+  }
+
+  /**
+   * Performs a redirect if the path changed in routing.
+   *
+   * For example, when language negotiation selected a different language for
+   * the page.
+   *
+   * @param \Symfony\Component\HttpKernel\Event\GetResponseEvent $event
+   *   The Event to process.
+   */
+  public function onKernelRequestRedirect(GetResponseEvent $event) {
+    $request = $event->getRequest();
+    $can_redirect = $event->isMasterRequest()
+      && $request->isMethod('GET')
+      && !$request->query->has('destination')
+      && !$this->isRequestChanged($request);
+    if ($can_redirect) {
+      // Construct URL to the current route. If it is different from the request
+      // URL, then we assume that it was changed on a purpose (for example, to
+      // match the detected language) and perform a redirect.
+      $route_name = $this->pathMatcher->isFrontPage() ? '<front>' : '<current>';
+      $options = [
+        'query' => $request->query->all(),
+        'absolute' => TRUE,
+      ];
+      $redirect_uri = $this->urlGenerator->generateFromRoute($route_name, [], $options);
+      $original_uri = $request->getSchemeAndHttpHost() . $request->getRequestUri();
+      if ($redirect_uri != $original_uri) {
+        $event->setResponse(new RedirectResponse($redirect_uri));
+      }
+    }
+  }
+
+  /**
+   * Registers the methods in this class that should be listeners.
+   *
+   * @return array
+   *   An array of event listener definitions.
+   */
+  static function getSubscribedEvents() {
+    // Execute after routes are initialized in
+    // \Drupal\Core\Routing\RoutePreloader::onRequest().
+    $events[KernelEvents::REQUEST][] = array('onKernelRequestRedirect', -1);
+
+    return $events;
+  }
+
+  /**
+   * Checks if given request is different from the initial one.
+   *
+   * Some code can change the request object, for example, during the inbound
+   * path processing. Mostly the request attributes are used, but in some cases
+   * the request query can be changed. If this happens, we can't construct a
+   * redirect.
+   *
+   * @param \Symfony\Component\HttpFoundation\Request $request
+   *   The request object passed from the KernelEvents::REQUEST event.
+   *
+   * @return bool
+   */
+  protected function isRequestChanged(Request $request) {
+    if (!isset($this->requestFromGlobals)) {
+      $this->requestFromGlobals = Request::createFromGlobals();
+    }
+    return $request->query->all() != $this->requestFromGlobals->query->all();
+  }
+
+}
diff --git a/core/lib/Drupal/Core/Routing/UrlGenerator.php b/core/lib/Drupal/Core/Routing/UrlGenerator.php
index 9979b73..c9521ed 100644
--- a/core/lib/Drupal/Core/Routing/UrlGenerator.php
+++ b/core/lib/Drupal/Core/Routing/UrlGenerator.php
@@ -235,10 +235,8 @@ protected function doGenerate(array $variables, array $defaults, array $tokens,
 
     // Add a query string if needed, including extra parameters.
     $query_params += array_diff_key($parameters, $variables, $defaults);
-    if ($query_params && $query = http_build_query($query_params, '', '&')) {
-      // "/" and "?" can be left decoded for better user experience, see
-      // http://tools.ietf.org/html/rfc3986#section-3.4
-      $url .= '?'.strtr($query, array('%2F' => '/'));
+    if ($query_params && $query = UrlHelper::buildQuery($query_params)) {
+      $url .= '?' . $query;
     }
 
     return $url;
@@ -300,7 +298,7 @@ public function generateFromRoute($name, $parameters = array(), $options = array
 
     // Generate a relative URL having no path, just query string and fragment.
     if ($route->getOption('_no_path')) {
-      $query = $query_params ? '?' . http_build_query($query_params, '', '&') : '';
+      $query = $query_params ? '?' . UrlHelper::buildQuery($query_params) : '';
       $url = $query . $fragment;
       return $collect_bubbleable_metadata ? $generated_url->setGeneratedUrl($url) : $url;
     }
diff --git a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php
index fd9da35..126dc1c 100644
--- a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php
+++ b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationContentEntity.php
@@ -123,10 +123,12 @@ public function processOutbound($path, &$options = [], Request $request = NULL,
         unset($options['language']);
       }
 
-      if (isset($options['query']) && is_string($options['query'])) {
-        $query = [];
-        parse_str($options['query'], $query);
-        $options['query'] = $query;
+      if (isset($options['query'])) {
+        if (is_string($options['query'])) {
+          $query = [];
+          parse_str($options['query'], $query);
+          $options['query'] = $query;
+        }
       }
       else {
         $options['query'] = [];
diff --git a/core/modules/simpletest/src/WebTestBase.php b/core/modules/simpletest/src/WebTestBase.php
index 1e3bfdb..c739fc5 100644
--- a/core/modules/simpletest/src/WebTestBase.php
+++ b/core/modules/simpletest/src/WebTestBase.php
@@ -2189,7 +2189,7 @@ protected function translatePostValues(array $values) {
     // The easiest and most straightforward way to translate values suitable for
     // WebTestBase::drupalPostForm() is to actually build the POST data string
     // and convert the resulting key/value pairs back into a flat array.
-    $query = http_build_query($values);
+    $query = UrlHelper::buildQuery($values);
     foreach (explode('&', $query) as $item) {
       list($key, $value) = explode('=', $item);
       $edit[urldecode($key)] = urldecode($value);
diff --git a/core/modules/statistics/src/Tests/StatisticsReportsTest.php b/core/modules/statistics/src/Tests/StatisticsReportsTest.php
index f2a79ff..2dbfa8d 100644
--- a/core/modules/statistics/src/Tests/StatisticsReportsTest.php
+++ b/core/modules/statistics/src/Tests/StatisticsReportsTest.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\statistics\Tests;
+use Drupal\Component\Utility\UrlHelper;
 
 /**
  * Tests display of statistics report blocks.
@@ -26,7 +27,7 @@ function testPopularContentBlock() {
     $this->drupalGet('node/' . $node->id());
     // Manually calling statistics.php, simulating ajax behavior.
     $nid = $node->id();
-    $post = http_build_query(array('nid' => $nid));
+    $post = UrlHelper::buildQuery(array('nid' => $nid));
     $headers = array('Content-Type' => 'application/x-www-form-urlencoded');
     global $base_url;
     $stats_path = $base_url . '/' . drupal_get_path('module', 'statistics'). '/statistics.php';
diff --git a/core/modules/statistics/src/Tests/StatisticsTokenReplaceTest.php b/core/modules/statistics/src/Tests/StatisticsTokenReplaceTest.php
index 792c40a..f7888d4 100644
--- a/core/modules/statistics/src/Tests/StatisticsTokenReplaceTest.php
+++ b/core/modules/statistics/src/Tests/StatisticsTokenReplaceTest.php
@@ -6,6 +6,7 @@
  */
 
 namespace Drupal\statistics\Tests;
+use Drupal\Component\Utility\UrlHelper;
 
 /**
  * Generates text using placeholders for dummy content to check statistics token
@@ -29,7 +30,7 @@ function testStatisticsTokenReplacement() {
     $this->drupalGet('node/' . $node->id());
     // Manually calling statistics.php, simulating ajax behavior.
     $nid = $node->id();
-    $post = http_build_query(array('nid' => $nid));
+    $post = UrlHelper::buildQuery(array('nid' => $nid));
     $headers = array('Content-Type' => 'application/x-www-form-urlencoded');
     global $base_url;
     $stats_path = $base_url . '/' . drupal_get_path('module', 'statistics'). '/statistics.php';
diff --git a/core/modules/system/src/Tests/Common/UrlTest.php b/core/modules/system/src/Tests/Common/UrlTest.php
index f52d022..3c43406 100644
--- a/core/modules/system/src/Tests/Common/UrlTest.php
+++ b/core/modules/system/src/Tests/Common/UrlTest.php
@@ -313,12 +313,12 @@ function testExternalUrls() {
     $url = $test_url;
     $query = array($this->randomMachineName(5) => $this->randomMachineName(5));
     $result = Url::fromUri($url, array('query' => $query))->toString();
-    $this->assertEqual($url . '?' . http_build_query($query, '', '&'), $result, 'External URL can be extended with a query string in $options.');
+    $this->assertEqual($url . '?' . UrlHelper::buildQuery($query), $result, 'External URL can be extended with a query string in $options.');
 
     // Verify query string can be extended in an external URL.
     $url = $test_url . '?drupal=awesome';
     $query = array($this->randomMachineName(5) => $this->randomMachineName(5));
     $result = Url::fromUri($url, array('query' => $query))->toString();
-    $this->assertEqual($url . '&' . http_build_query($query, '', '&'), $result);
+    $this->assertEqual($url . '&' . UrlHelper::buildQuery($query), $result);
   }
 }
diff --git a/core/modules/system/src/Tests/Routing/ContentNegotiationRoutingTest.php b/core/modules/system/src/Tests/Routing/ContentNegotiationRoutingTest.php
index 98515b8..416b11c 100644
--- a/core/modules/system/src/Tests/Routing/ContentNegotiationRoutingTest.php
+++ b/core/modules/system/src/Tests/Routing/ContentNegotiationRoutingTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\system\Tests\Routing;
 
+use Drupal\Component\Utility\UrlHelper;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\simpletest\KernelTestBase;
 use Symfony\Component\HttpFoundation\Request;
@@ -113,6 +114,18 @@ function testContentRouting() {
       // Verbose message since simpletest doesn't let us provide a message and
       // see the error.
       $this->assertTrue(TRUE, $message);
+
+      // Handle redirect.
+      if ($response->isRedirect()) {
+        $parsed = parse_url($response->headers->get('Location'));
+        $path = $parsed['path'];
+        if (isset($parsed['query'])) {
+          $path .= '?' . $parsed['query'];
+        }
+        $request = Request::create($path);
+        $response = $kernel->handle($request);
+      }
+
       $this->assertEqual($response->getStatusCode(), Response::HTTP_OK);
       $this->assertTrue(strpos($response->headers->get('Content-type'), $content_type) !== FALSE);
     }