diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 27573e70aff41762492e39f6b96f820c76dca3ca..5f584196b184be974ebfb398837c0c72c5c4c7d6 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1343,8 +1343,15 @@ function template_preprocess_html(&$variables) {
   // Add a variable for the root path. This can be used to create a class and
   // theme the page depending on the current path (e.g. node, admin, user) as
   // well as more specific data like path-frontpage.
-  $path = \Drupal::request()->getPathInfo();
-  $variables['root_path'] = explode('/', $path)[1];
+  $is_front_page =  \Drupal::service('path.matcher')->isFrontPage();
+
+  if ($is_front_page) {
+    $variables['root_path'] = TRUE;
+  }
+  else {
+    $system_path = \Drupal::request()->attributes->get('_system_path');
+    $variables['root_path'] = explode('/', $system_path)[0];
+  }
 
   $site_config = \Drupal::config('system.site');
   // Construct page title.
@@ -1356,7 +1363,7 @@ function template_preprocess_html(&$variables) {
   }
   // @todo Remove once views is not bypassing the view subscriber anymore.
   //   @see http://drupal.org/node/2068471
-  elseif (drupal_is_front_page()) {
+  elseif ($is_front_page) {
     $head_title = array(
       'title' => t('Home'),
       'name' => String::checkPlain($site_config->get('name')),
diff --git a/core/modules/language/src/Tests/LanguageSwitchingTest.php b/core/modules/language/src/Tests/LanguageSwitchingTest.php
index a39da666357a7d808c4a9799f2c1326c11d93ad7..d0e2a0d0e300f3dbfc5d2e22479a6aad65907235 100644
--- a/core/modules/language/src/Tests/LanguageSwitchingTest.php
+++ b/core/modules/language/src/Tests/LanguageSwitchingTest.php
@@ -163,7 +163,6 @@ protected function doTestLanguageBlockAnonymous($block_label) {
   /**
    * Test languge switcher links for domain based negotiation
    */
-
   function testLanguageBlockWithDomain() {
     // Add the Italian language.
     ConfigurableLanguage::createFromLangcode('it')->save();
@@ -241,6 +240,33 @@ function testLanguageLinkActiveClass() {
     $this->doTestLanguageLinkActiveClassAnonymous();
   }
 
+  /**
+   * Check the path-admin class, as same as on default language.
+   */
+  function testLanguageBodyClass() {
+    $searched_class = 'path-admin';
+
+    // Add language.
+    $edit = array(
+      'predefined_langcode' => 'fr',
+    );
+    $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add language'));
+
+    // Enable URL language detection and selection.
+    $edit = array('language_interface[enabled][language-url]' => '1');
+    $this->drupalPostForm('admin/config/regional/language/detection', $edit, t('Save settings'));
+
+    // Go to admin/config, check the class on default language.
+    $this->drupalGet('admin/config');
+    $class = $this->xpath('//body[contains(@class, :class)]', array(':class' => $searched_class));
+    $this->assertTrue(isset($class[0]), t('The path-admin class appears on default language.'));
+
+    // Go to admin/config, check the class on french language.
+    $this->drupalGet('fr/admin/config');
+    $class = $this->xpath('//body[contains(@class, :class)]', array(':class' => $searched_class));
+    $this->assertTrue(isset($class[0]), t('The path-admin class same as on default language.'));
+  }
+
   /**
    * For authenticated users, the "active" class is set by JavaScript.
    *