diff -u b/core/misc/message.js b/core/misc/message.js
--- b/core/misc/message.js
+++ b/core/misc/message.js
@@ -70,33 +70,28 @@
      *
      * @name Drupal.message~messageDefinition.remove
      *
-     * @param {string|number} [messageIndex]
+     * @param {Number|String|Array.<string|number>} [messages]
      *   Index of the message to remove, as returned by
-     *   {@link Drupal.message~messageDefinition.add} or a number
-     *   corresponding to the CSS index of the element.
+     *   {@link Drupal.message~messageDefinition.add}, a number
+     *   corresponding to the CSS index of the element, or an
+     *   array containing a combination of the previous two types.
      *
      * @return {number}
      *  Number of removed messages.
      */
-    function messageRemove(messageIndex) {
-      var removeSelector = '[data-drupal-message]';
+    function messageRemove(messages) {
+      var messagesToRemove = messages instanceof Array ? messages : [messages];
+      messagesToRemove.forEach(function (messageIndex) {
+        var removeSelector = typeof messageIndex === 'string' ?
+          // If it's a string, select corresponding message.
+          '[data-drupal-message="' + messageIndex + '"]' :
+          // If the index is numeric remove the element based on the DOM index.
+          '[data-drupal-message]:nth-child(' + messageIndex + ')';
+        var remove = this.element.querySelector(removeSelector);
+        this.element.removeChild(remove);
+      }.bind(this));
 
-      // If it's a string, select corresponding message.
-      if (typeof messageIndex === 'string') {
-        removeSelector = '[data-drupal-message="' + messageIndex + '"]';
-      }
-      // If the index is numeric remove the element based on the DOM index.
-      else if (typeof messageIndex === 'number') {
-        removeSelector = '[data-drupal-message]:nth-child(' + messageIndex + ')';
-      }
-
-      var remove = this.element.querySelectorAll(removeSelector);
-      var length = remove.length;
-      for (var i = 0; i < length; i += 1) {
-        this.element.removeChild(remove[i]);
-      }
-
-      return length;
+      return messagesToRemove.length;
     }
 
     return {
diff -u b/core/modules/system/src/Tests/JsMessageTestCases.php b/core/modules/system/src/Tests/JsMessageTestCases.php
--- b/core/modules/system/src/Tests/JsMessageTestCases.php
+++ b/core/modules/system/src/Tests/JsMessageTestCases.php
@@ -8,16 +8,6 @@
 class JsMessageTestCases {
 
   /**
-   * Gets the test contexts.
-   *
-   * @return string[]
-   *   The test contexts.
-   */
-  public static function getContexts() {
-    return ['context1', 'context2'];
-  }
-
-  /**
    * Gets the test types.
    *
    * @return string[]
diff -u b/core/modules/system/tests/modules/js_message_test/js/js_message_test.js b/core/modules/system/tests/modules/js_message_test/js/js_message_test.js
--- b/core/modules/system/tests/modules/js_message_test/js/js_message_test.js
+++ b/core/modules/system/tests/modules/js_message_test/js/js_message_test.js
@@ -3,7 +3,7 @@
  *  Testing behavior for JSMessageTest.
  */
 
-(function ($, message) {
+(function ($) {
 
   'use strict';
 
@@ -18,31 +18,47 @@
-      var message = Drupal.message();
-      var messageIndex;
-      var messageList = [];
+      var messageObjects = {};
+      var messageIndexes = {};
+
       $('.show-link').once('show-msg').on('click', function (e) {
+
         e.preventDefault();
         var type = e.currentTarget.getAttribute('data-type');
-        messageIndex = message.add('Msg-' + type, type);
+        messageIndexes[type] = getMessageObject(e).add('Msg-' + type, type);
       });
       $('.remove-link').once('remove-msg').on('click', function (e) {
         e.preventDefault();
         var type = e.currentTarget.getAttribute('data-type');
-        message.remove(messageIndex);
+        getMessageObject(e).remove(messageIndexes[type]);
       });
       $('.show-multiple').once('show-msg').on('click', function (e) {
         e.preventDefault();
         for (var i = 0; i < 10; i++) {
-          messageList.push(message.add('Msg-' + i, 'status'));
+          messageIndexes[i] = getMessageObject(e).add('Msg-' + i, 'status');
         }
 
       });
       $('.remove-multiple').once('remove-msg').on('click', function (e) {
         e.preventDefault();
         for (var i = 0; i < 10; i++) {
-          message.remove(messageList[i]);
+          getMessageObject(e).remove(messageIndexes[i]);
         }
-        messageList = [];
       });
+
+      /**
+       * Gets message object for the click event.
+       *
+       * @param {jQuery.Event} e
+       *   The click event.
+       * @return {Drupal.message~messageDefinition}
+       *  The message object for correct div.
+       */
+      function getMessageObject(e) {
+        var divSelector = e.currentTarget.getAttribute('data-selector');
+        if (!messageObjects.hasOwnProperty(divSelector)) {
+          messageObjects[divSelector] = Drupal.message(document.querySelector(divSelector));
+        }
+        return messageObjects[divSelector];
+      }
     }
   };
 
-})(jQuery, Drupal.message);
+})(jQuery);
diff -u b/core/modules/system/tests/modules/js_message_test/src/Controller/JSMessageTestController.php b/core/modules/system/tests/modules/js_message_test/src/Controller/JSMessageTestController.php
--- b/core/modules/system/tests/modules/js_message_test/src/Controller/JSMessageTestController.php
+++ b/core/modules/system/tests/modules/js_message_test/src/Controller/JSMessageTestController.php
@@ -19,41 +19,36 @@
   public function messageLinks() {
     $links = [];
     foreach (JsMessageTestCases::getMessagesSelectors() as $messagesSelector) {
-      foreach (JsMessageTestCases::getContexts() as $context) {
-        foreach (JsMessageTestCases::getTypes() as $type) {
-          $links["show-$messagesSelector-$context-$type"] = [
-            'title' => "Show-$messagesSelector-$context-$type",
-            'url' => Url::fromRoute('js_message_test.links'),
-            'attributes' => [
-              'id' => "show-$messagesSelector-$context-$type",
-              'data-context' => $context,
-              'data-type' => $type,
-              'data-selector' => $messagesSelector,
-              'class' => ['show-link'],
-            ],
-          ];
-          $links["remove-$messagesSelector-$context-$type"] = [
-            'title' => "Remove-$messagesSelector-$context-$type",
-            'url' => Url::fromRoute('js_message_test.links'),
-            'attributes' => [
-              'id' => "remove-$messagesSelector-$context-$type",
-              'data-context' => $context,
-              'data-type' => $type,
-              'data-selector' => $messagesSelector,
-              'class' => ['remove-link'],
-            ],
-          ];
-        }
-        $links["remove-$context"] = [
-          'title' => "Remove-$context-all",
+      foreach (JsMessageTestCases::getTypes() as $type) {
+        $links["show-$messagesSelector-$type"] = [
+          'title' => "Show-$messagesSelector-$type",
           'url' => Url::fromRoute('js_message_test.links'),
           'attributes' => [
-            'id' => "remove-$context",
-            'data-context' => $context,
+            'id' => "show-$messagesSelector-$type",
+            'data-type' => $type,
+            'data-selector' => $messagesSelector,
+            'class' => ['show-link'],
+          ],
+        ];
+        $links["remove-$messagesSelector-$type"] = [
+          'title' => "Remove-$messagesSelector-$type",
+          'url' => Url::fromRoute('js_message_test.links'),
+          'attributes' => [
+            'id' => "remove-$messagesSelector-$type",
+            'data-type' => $type,
+            'data-selector' => $messagesSelector,
             'class' => ['remove-link'],
           ],
         ];
       }
+      $links["remove"] = [
+        'title' => "Remove-all",
+        'url' => Url::fromRoute('js_message_test.links'),
+        'attributes' => [
+          'id' => "remove",
+          'class' => ['remove-link'],
+        ],
+      ];
     }
 
     $links['show-multi'] = [
diff -u b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
--- b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/JsMessageTest.php
@@ -17,6 +17,9 @@
    */
   public static $modules = ['js_message_test'];
 
+  /**
+   * {@inheritdoc}
+   */
   protected function setUp() {
     parent::setUp();
 
@@ -27,7 +30,6 @@
     $theme_config->save();
   }
 
-
   /**
    * Test click on links to show messages and remove messages.
    */
@@ -35,49 +37,31 @@
     $web_assert = $this->assertSession();
     $this->drupalGet('js_message_test_link');
 
+    $current_messages = [];
     foreach (JsMessageTestCases::getMessagesSelectors() as $messagesSelector) {
       $web_assert->elementExists('css', $messagesSelector);
-      foreach (JsMessageTestCases ::getContexts() as $context) {
-        foreach (JsMessageTestCases::getTypes() as $type) {
-          $this->clickLink("Show-$messagesSelector-$context-$type");
-          $selector = "$messagesSelector .messages.messages--$type.js-messages.js-messages-context--$context";
-          $msg_element = $web_assert->waitForElementVisible('css', $selector);
-          $this->assertNotEmpty($msg_element, "Message element visible: $selector");
-          $web_assert->elementContains('css', $selector, "Msg-$context-$type");
-          // Click all remove links except the one that will remove the message.
-          $this->clickAllRemoveLinksExcept($context, $type, $messagesSelector);
-          // Confirm the message was not removed.
-          $web_assert->elementContains('css', $selector, "Msg-$context-$type");
-          // Click the remove links that should remove the message.
-          $this->clickLink("Remove-$messagesSelector-$context-$type");
-          $web_assert->elementNotExists('css', $selector);
-        }
+      foreach (JsMessageTestCases::getTypes() as $type) {
+        $this->clickLink("Show-$messagesSelector-$type");
+        $selector = "$messagesSelector .messages.messages--$type";
+        $msg_element = $web_assert->waitForElementVisible('css', $selector);
+        $this->assertNotEmpty($msg_element, "Message element visible: $selector");
+        $web_assert->elementContains('css', $selector, "Msg-$type");
+        $current_messages[$selector] = "Msg-$type";
+        $this->assertCurrentMessages($current_messages);
+      }
+      // Remove messages 1 by 1 and confirm the messages are expected.
+      foreach (JsMessageTestCases::getTypes() as $type) {
+        $this->clickLink("Remove-$messagesSelector-$type");
+        $selector = "$messagesSelector .messages.messages--$type";
+        // The message for this selector should not be on the page.
+        unset($current_messages[$selector]);
+        $this->assertCurrentMessages($current_messages);
       }
-      // Test removing all messages of a specific context.
-      $this->clickLink("Show-$messagesSelector-context1-error");
-      $this->clickLink("Show-$messagesSelector-context2-error");
-      $this->clickLink("Show-$messagesSelector-context1-warning");
-      $this->clickLink("Show-$messagesSelector-context2-warning");
-      $this->waitForMessageElement('warning', 'context2');
-      $this->assertCurrentMessages([
-        'Msg-context1-error',
-        'Msg-context2-error',
-        'Msg-context1-warning',
-        'Msg-context2-warning',
-      ]);
-      $this->clickLink('Remove-context1-all');
-      $web_assert->assertWaitOnAjaxRequest();
-      $this->assertCurrentMessages([
-        'Msg-context2-error',
-        'Msg-context2-warning',
-      ]);
-      $this->clickLink('Remove-context2-all');
-      $this->assertCurrentMessages([]);
     }
+
     // Test adding multiple messages at once.
     // @see processMessages()
     $this->clickLink('Show Multiple');
-    $this->waitForMessageElement('status', 'context-9');
 
     $current_messages = [];
     for ($i = 0; $i < 10; $i++) {
@@ -86,27 +70,6 @@
     $this->assertCurrentMessages($current_messages);
     $this->clickLink('Remove Multiple');
     $this->assertCurrentMessages([]);
-
-
-
-  }
-
-  /**
-   * Clicks all remove message links except for combination specified.
-   *
-   * @param string $exclude_context
-   *   The message context to exclude.
-   * @param string $exclude_type
-   *   The message type to exclude.
-   */
-  protected function clickAllRemoveLinksExcept($exclude_context, $exclude_type, $messagesSelector) {
-    foreach (JsMessageTestCases::getContexts() as $context) {
-      foreach (JsMessageTestCases::getTypes() as $type) {
-        if ($context !== $exclude_context || $type !== $exclude_type) {
-          $this->clickLink("Remove-$messagesSelector-$context-$type");
-        }
-      }
-    }
   }
 
   /**
@@ -116,6 +79,7 @@
    *   Expected messages.
    */
   protected function assertCurrentMessages(array $expected_messages) {
+    $expected_messages = array_values($expected_messages);
     $current_messages = [];
     if ($message_divs = $this->getSession()->getPage()->findAll('css', '.messages')) {
       foreach ($message_divs as $message_div) {
@@ -128,15 +92,2 @@
 
-  /**
-   * Waits for an element message to be visible.
-   *
-   * @param string $type
-   *   The type of the message.
-   * @param string $context
-   *   The context of the message.
-   */
-  protected function waitForMessageElement($type, $context) {
-    $last_msg_element = $this->assertSession()->waitForElementVisible('css', ".messages.messages--$type.js-messages.js-messages-context--$context");
-    $this->assertNotEmpty($last_msg_element, "Message element visible.");
-  }
-
 }
only in patch2:
unchanged:
--- a/core/lib/Drupal/Core/Entity/ContentEntityBase.php
+++ b/core/lib/Drupal/Core/Entity/ContentEntityBase.php
@@ -1094,8 +1094,7 @@ public function __clone() {
 
     // Ensure that the following properties are actually cloned by
     // overwriting the original references with ones pointing to copies of
-    // them: enforceIsNew, newRevision, loadedRevisionId, fields, entityKeys and
-    // translatableEntityKeys.
+    // them: enforceIsNew, newRevision, loadedRevisionId and fields.
     $enforce_is_new = $this->enforceIsNew;
     $this->enforceIsNew = &$enforce_is_new;
 
@@ -1108,12 +1107,6 @@ public function __clone() {
     $fields = $this->fields;
     $this->fields = &$fields;
 
-    $entity_keys = $this->entityKeys;
-    $this->entityKeys = &$entity_keys;
-
-    $translatable_entity_keys = $this->translatableEntityKeys;
-    $this->translatableEntityKeys = &$translatable_entity_keys;
-
     foreach ($this->fields as $name => $values) {
       $this->fields[$name] = [];
       // Untranslatable fields may have multiple references for the same field
only in patch2:
unchanged:
--- a/core/modules/language/src/LanguageNegotiatorInterface.php
+++ b/core/modules/language/src/LanguageNegotiatorInterface.php
@@ -91,6 +91,7 @@
  *     }
  *   }
  * }
+ * ?>
  * @endcode
  *
  * For more information, see
only in patch2:
unchanged:
--- a/core/modules/user/src/Tests/UserTimeZoneTest.php
+++ b/core/modules/user/src/Tests/UserTimeZoneTest.php
@@ -28,15 +28,8 @@ public function testUserTimeZone() {
       ->set('timezone.user.configurable', 1)
       ->set('timezone.default', 'America/Los_Angeles')
       ->save();
-
-    // Load the 'medium' date format, which is the default for node creation
-    // time, and override it. Since we are testing time zones with Daylight
-    // Saving Time, and need to future proof against changes to the zoneinfo
-    // database, we choose the 'I' format placeholder instead of a
-    // human-readable zone name. With 'I', a 1 means the date is in DST, and 0
-    // if not.
     DateFormat::load('medium')
-      ->setPattern('Y-m-d H:i I')
+      ->setPattern('Y-m-d H:i T')
       ->save();
 
     // Create a user account and login.
@@ -56,11 +49,11 @@ public function testUserTimeZone() {
 
     // Confirm date format and time zone.
     $this->drupalGet('node/' . $node1->id());
-    $this->assertText('2007-03-09 21:00 0', 'Date should be PST.');
+    $this->assertText('2007-03-09 21:00 PST', 'Date should be PST.');
     $this->drupalGet('node/' . $node2->id());
-    $this->assertText('2007-03-11 01:00 0', 'Date should be PST.');
+    $this->assertText('2007-03-11 01:00 PST', 'Date should be PST.');
     $this->drupalGet('node/' . $node3->id());
-    $this->assertText('2007-03-20 21:00 1', 'Date should be PDT.');
+    $this->assertText('2007-03-20 21:00 PDT', 'Date should be PDT.');
 
     // Change user time zone to Santiago time.
     $edit = [];
@@ -71,25 +64,25 @@ public function testUserTimeZone() {
 
     // Confirm date format and time zone.
     $this->drupalGet('node/' . $node1->id());
-    $this->assertText('2007-03-10 02:00 1', 'Date should be Chile summer time; five hours ahead of PST.');
+    $this->assertText('2007-03-10 02:00 CLST', 'Date should be Chile summer time; five hours ahead of PST.');
     $this->drupalGet('node/' . $node2->id());
-    $this->assertText('2007-03-11 05:00 0', 'Date should be Chile time; four hours ahead of PST');
+    $this->assertText('2007-03-11 05:00 CLT', 'Date should be Chile time; four hours ahead of PST');
     $this->drupalGet('node/' . $node3->id());
-    $this->assertText('2007-03-21 00:00 0', 'Date should be Chile time; three hours ahead of PDT.');
+    $this->assertText('2007-03-21 00:00 CLT', 'Date should be Chile time; three hours ahead of PDT.');
 
     // Ensure that anonymous users also use the default timezone.
     $this->drupalLogout();
     $this->drupalGet('node/' . $node1->id());
-    $this->assertText('2007-03-09 21:00 0', 'Date should be PST.');
+    $this->assertText('2007-03-09 21:00 PST', 'Date should be PST.');
     $this->drupalGet('node/' . $node2->id());
-    $this->assertText('2007-03-11 01:00 0', 'Date should be PST.');
+    $this->assertText('2007-03-11 01:00 PST', 'Date should be PST.');
     $this->drupalGet('node/' . $node3->id());
-    $this->assertText('2007-03-20 21:00 1', 'Date should be PDT.');
+    $this->assertText('2007-03-20 21:00 PDT', 'Date should be PDT.');
 
     // Format a date without accessing the current user at all and
     // ensure that it uses the default timezone.
     $this->drupalGet('/system-test/date');
-    $this->assertText('2016-01-13 08:29 0', 'Date should be PST.');
+    $this->assertText('2016-01-13 08:29 PST', 'Date should be PST.');
   }
 
 }
only in patch2:
unchanged:
--- a/core/tests/Drupal/KernelTests/Core/Entity/ContentEntityCloneTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/ContentEntityCloneTest.php
@@ -179,44 +179,4 @@ public function testNewRevisionOnCloneEntityTranslation() {
     $this->assertFalse($entity_translation->isNewRevision());
   }
 
-  /**
-   * Tests modifications on entity keys of a cloned entity object.
-   */
-  public function testEntityKeysModifications() {
-    // Create a test entity with a translation, which will internally trigger
-    // entity cloning for the new translation and create references for some of
-    // the entity properties.
-    $entity = EntityTestMulRev::create([
-      'name' => 'original-name',
-      'uuid' => 'original-uuid',
-      'language' => 'en',
-    ]);
-    $entity->addTranslation('de');
-    $entity->save();
-
-    // Clone the entity.
-    $clone = clone $entity;
-
-    // Alter a non-translatable and a translatable entity key fields of the
-    // cloned entity and assert that retrieving the value through the entity
-    // keys local cache will be different for the cloned and the original
-    // entity.
-    // We first have to call the ::uuid() and ::label() method on the original
-    // entity as it is going to cache the field values into the $entityKeys and
-    // $translatableEntityKeys properties of the entity object and we want to
-    // check that the cloned and the original entity aren't sharing the same
-    // reference to those local cache properties.
-    $uuid_field_name = $entity->getEntityType()->getKey('uuid');
-    $this->assertFalse($entity->getFieldDefinition($uuid_field_name)->isTranslatable());
-    $clone->$uuid_field_name->value = 'clone-uuid';
-    $this->assertEquals('original-uuid', $entity->uuid());
-    $this->assertEquals('clone-uuid', $clone->uuid());
-
-    $label_field_name = $entity->getEntityType()->getKey('label');
-    $this->assertTrue($entity->getFieldDefinition($label_field_name)->isTranslatable());
-    $clone->$label_field_name->value = 'clone-name';
-    $this->assertEquals('original-name', $entity->label());
-    $this->assertEquals('clone-name', $clone->label());
-  }
-
 }