diff --git a/core/modules/language/src/Plugin/Block/LanguageBlock.php b/core/modules/language/src/Plugin/Block/LanguageBlock.php
index 3995ece..bb9455b 100644
--- a/core/modules/language/src/Plugin/Block/LanguageBlock.php
+++ b/core/modules/language/src/Plugin/Block/LanguageBlock.php
@@ -10,6 +10,8 @@
 use Drupal\Core\Access\AccessResult;
 use Drupal\Core\Block\BlockBase;
 use Drupal\Core\Path\PathMatcherInterface;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\language\LanguageNegotiatorInterface;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Language\LanguageManagerInterface;
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
@@ -36,6 +38,12 @@ class LanguageBlock extends BlockBase implements ContainerFactoryPluginInterface
   protected $languageManager;
 
   /**
+   * The language negotiator.
+   * @var \Drupal\language\LanguageNegotiatorInterface
+   */
+  protected $negotiator;
+
+  /**
    * The path matcher.
    *
    * @var \Drupal\Core\Path\PathMatcherInterface
@@ -55,11 +63,14 @@ class LanguageBlock extends BlockBase implements ContainerFactoryPluginInterface
    *   The language manager.
    * @param \Drupal\Core\Path\PathMatcherInterface $path_matcher
    *   The path matcher.
+   * @param \Drupal\language\LanguageNegotiatorInterface $negotiator
+   *   The language negotiator.
    */
-  public function __construct(array $configuration, $plugin_id, $plugin_definition, LanguageManagerInterface $language_manager, PathMatcherInterface $path_matcher) {
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, LanguageManagerInterface $language_manager, PathMatcherInterface $path_matcher, LanguageNegotiatorInterface $negotiator) {
     parent::__construct($configuration, $plugin_id, $plugin_definition);
     $this->languageManager = $language_manager;
     $this->pathMatcher = $path_matcher;
+    $this->negotiator = $negotiator;
   }
 
 
@@ -72,7 +83,8 @@ public static function create(ContainerInterface $container, array $configuratio
       $plugin_id,
       $plugin_definition,
       $container->get('language_manager'),
-      $container->get('path.matcher')
+      $container->get('path.matcher'),
+      $container->get('language_negotiator')
     );
   }
 
@@ -118,4 +130,23 @@ public function getCacheMaxAge() {
     return 0;
   }
 
+  /**
+   * {@inheritdoc}
+   */
+  public function blockForm($form, FormStateInterface $form_state) {
+    $form = parent::blockForm($form, $form_state);
+    $languages = $this->languageManager->getLanguages();
+    // Warn the user that if only one language is enabled the block won't appear.
+    if (count($languages) == 1) {
+      drupal_set_message($this->t('Only one language is enabled. Therefore the language switcher block will not be shown. To add a new language on the site, go to @language-link.', array('@language-link' => \Drupal::l($this->t('Language list'), Url::fromRoute('entity.configurable_language.collection')))), 'warning');
+    }
+    // Warn the user that if there are no links to show because language-url
+    // method detection isn't enabled, the block won't appear.
+    elseif (!$this->negotiator->isNegotiationMethodEnabled('language-url')) {
+      drupal_set_message($this->t('No language detection method is enabled that would provide URL based detection. Therefore the language switcher block will not be shown.'), 'warning');
+    }
+
+    return $form;
+  }
+
 }
diff --git a/core/modules/language/src/Tests/LanguageSwitchingTest.php b/core/modules/language/src/Tests/LanguageSwitchingTest.php
index c9ff8d0..828f11a 100644
--- a/core/modules/language/src/Tests/LanguageSwitchingTest.php
+++ b/core/modules/language/src/Tests/LanguageSwitchingTest.php
@@ -283,6 +283,37 @@ function testLanguageBodyClass() {
 
   }
 
+  function testLanguageSwitcher() {
+    // Go to block layout.
+    $this->drupalGet('admin/structure/block');
+
+    // Check the link to add the block is there.
+    $language_switcher = $this->xpath('//*[@id="edit-category-system"]/div/ul/li[@class="language-blocklanguage-interface"]/a');
+    $this->assertTrue($language_switcher, 'Language  switcher is available.');
+
+    // Check the link has a tooltip.
+    $this->assertTrue($language_switcher[0]['title'], 'The tooltip is available.');
+
+    // Click to add the Language switcher.
+    $this->clickLink(t('Language switcher'));
+
+    // Post the block form.
+    $edit = array('region' => 'sidebar_first',);
+    $this->drupalPostForm(NULL, $edit, t('Save block'));
+
+    // Check the block has not been added.
+    $block = $this->xpath('//*[@id="blocks"]/tbody/tr[@class="draggable color-warning js-block-placed odd"]');
+    $this->assertFalse($block, 'The block is not added.');
+
+    // Check the message is being rendered.
+    // TODO: The system can show more than one message, check it in a loop.
+    $warning_messages = $this->xpath('//div[@class="region region-content"]/div[@class="messages messages--status"]/ul/li');
+    foreach($warning_messages as $warning) {
+      $warning_bool = ((string) $warning === 'The block Language Switcher cannot be added.') ? TRUE : FALSE;
+    }
+    $this->assertTrue($warning_bool, 'Message to warning the user the block cannot be added.');
+  }
+
   /**
    * For authenticated users, the "active" class is set by JavaScript.
    *