diff --git a/core/lib/Drupal/Component/Utility/SafeMarkup.php b/core/lib/Drupal/Component/Utility/SafeMarkup.php
index b4e0989..35166ff 100644
--- a/core/lib/Drupal/Component/Utility/SafeMarkup.php
+++ b/core/lib/Drupal/Component/Utility/SafeMarkup.php
@@ -128,20 +128,6 @@ public static function setMultiple(array $safe_strings) {
   }
 
   /**
-   * Encodes special characters in a plain-text string for display as HTML.
-   *
-   * @param string $string
-   *   A string.
-   *
-   * @return string
-   *   The escaped string. If $string was already set as safe with
-   *   self::set(), it won't be escaped again.
-   */
-  public static function escape($string) {
-    return static::isSafe($string) ? $string : static::checkPlain($string);
-  }
-
-  /**
   * Gets all strings currently marked as safe.
   *
   * This is useful for the batch and form APIs, where it is important to
@@ -229,13 +215,18 @@ public static function format($string, array $args) {
       switch ($key[0]) {
         case '@':
           // Escaped only.
-          $args[$key] = static::escape($value);
+          if (!SafeMarkup::isSafe($value)) {
+            $args[$key] = Html::escape($value);
+          }
           break;
 
         case '%':
         default:
           // Escaped and placeholder.
-          $args[$key] = '<em class="placeholder">' . static::escape($value) . '</em>';
+          if (!SafeMarkup::isSafe($value)) {
+            $value = Html::escape($value);
+          }
+          $args[$key] = '<em class="placeholder">' . $value . '</em>';
           break;
 
         case '!':
diff --git a/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
index 443cf73..533e98e 100644
--- a/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -142,7 +142,7 @@ public function getFilters() {
       // Implements safe joining.
       // @todo Make that the default for |join? Upstream issue:
       //   https://github.com/fabpot/Twig/issues/1420
-      new \Twig_SimpleFilter('safe_join', 'twig_drupal_join_filter', array('is_safe' => array('html'))),
+      new \Twig_SimpleFilter('safe_join', [$this, 'safeJoin'], ['needs_environment' => true, 'is_safe' => ['html']]),
 
       // Array filters.
       new \Twig_SimpleFilter('without', 'twig_without'),
@@ -514,4 +514,26 @@ public function renderVar($arg) {
     return $this->renderer->render($arg);
   }
 
+  /**
+   * Joins several strings together safely.
+   *
+   * @param \Twig_Environment $env
+   *   A Twig_Environment instance.
+   * @param mixed[]|\Traversable $value
+   *   The pieces to join.
+   * @param string $glue
+   *   The delimiter with which to join the string. Defaults to an empty string.
+   *   This value is expected to be safe for output and user provided data
+   *   should never be used as a glue.
+   *
+   * @return string
+   *   The strings joined together.
+   */
+  public function safeJoin(\Twig_Environment $env, $value, $glue = '') {
+    return implode($glue, array_map(function($item) use ($env) {
+      // If $item is not marked safe then it will be escaped.
+      return $this->escapeFilter($env, $item, 'html', NULL, TRUE);
+    }, $value));
+  }
+
 }
diff --git a/core/modules/content_translation/src/ContentTranslationHandler.php b/core/modules/content_translation/src/ContentTranslationHandler.php
index 10cf5f3..3979fff 100644
--- a/core/modules/content_translation/src/ContentTranslationHandler.php
+++ b/core/modules/content_translation/src/ContentTranslationHandler.php
@@ -290,8 +290,8 @@ public function entityFormAlter(array &$form, FormStateInterface $form_state, En
       $title = $this->entityFormTitle($entity);
       // When editing the original values display just the entity label.
       if ($form_langcode != $entity_langcode) {
-        $t_args = array('%language' => $languages[$form_langcode]->getName(), '%title' => $entity->label(), '!title' => $title);
-        $title = empty($source_langcode) ? t('!title [%language translation]', $t_args) : t('Create %language translation of %title', $t_args);
+        $t_args = array('%language' => $languages[$form_langcode]->getName(), '%title' => $entity->label(), '@title' => $title);
+        $title = empty($source_langcode) ? t('@title [%language translation]', $t_args) : t('Create %language translation of %title', $t_args);
       }
       $form['#title'] = $title;
     }
diff --git a/core/modules/system/src/Tests/Theme/TwigExtensionTest.php b/core/modules/system/src/Tests/Theme/TwigExtensionTest.php
index 7e25ae5..7ca45fb 100644
--- a/core/modules/system/src/Tests/Theme/TwigExtensionTest.php
+++ b/core/modules/system/src/Tests/Theme/TwigExtensionTest.php
@@ -47,6 +47,8 @@ function testTwigExtensionFilter() {
 
     $this->drupalGet('twig-extension-test/filter');
     $this->assertText('Every plant is not a mineral.', 'Success: String filtered.');
+    // Test safe_join filter.
+    $this->assertRaw('&lt;em&gt;will be escaped&lt;/em&gt;<br/><em>will be markup</em><br/><strong>will be rendered</strong>');
   }
 
   /**
diff --git a/core/modules/system/tests/modules/batch_test/batch_test.callbacks.inc b/core/modules/system/tests/modules/batch_test/batch_test.callbacks.inc
index 461219f..026c8a7 100644
--- a/core/modules/system/tests/modules/batch_test/batch_test.callbacks.inc
+++ b/core/modules/system/tests/modules/batch_test/batch_test.callbacks.inc
@@ -5,7 +5,7 @@
  * Batch callbacks for the Batch API tests.
  */
 
-use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Component\Utility\Html;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\RedirectResponse;
 
@@ -90,7 +90,7 @@ function _batch_test_nested_batch_callback() {
 function _batch_test_finished_helper($batch_id, $success, $results, $operations) {
   if ($results) {
     foreach ($results as $op => $op_results) {
-      $messages[] = 'op '. SafeMarkup::escape($op) . ': processed ' . count($op_results) . ' elements';
+      $messages[] = 'op '. Html::escape($op) . ': processed ' . count($op_results) . ' elements';
     }
   }
   else {
diff --git a/core/modules/system/tests/modules/twig_extension_test/src/TwigExtensionTestController.php b/core/modules/system/tests/modules/twig_extension_test/src/TwigExtensionTestController.php
index 4ff849a..bbfe65e 100644
--- a/core/modules/system/tests/modules/twig_extension_test/src/TwigExtensionTestController.php
+++ b/core/modules/system/tests/modules/twig_extension_test/src/TwigExtensionTestController.php
@@ -7,10 +7,13 @@
 
 namespace Drupal\twig_extension_test;
 
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+
 /**
  * Controller routines for Twig extension test routes.
  */
 class TwigExtensionTestController {
+  use StringTranslationTrait;
 
   /**
    * Menu callback for testing Twig filters in a Twig template.
@@ -19,6 +22,11 @@ public function testFilterRender() {
     return array(
       '#theme' => 'twig_extension_test_filter',
       '#message' => 'Every animal is not a mineral.',
+      '#safe_join_items' => [
+        '<em>will be escaped</em>',
+        $this->t('<em>will be markup</em>'),
+        ['#markup' => '<strong>will be rendered</strong>']
+      ]
     );
   }
 
diff --git a/core/modules/system/tests/modules/twig_extension_test/templates/twig_extension_test.filter.html.twig b/core/modules/system/tests/modules/twig_extension_test/templates/twig_extension_test.filter.html.twig
index 1e224d0..981874f 100644
--- a/core/modules/system/tests/modules/twig_extension_test/templates/twig_extension_test.filter.html.twig
+++ b/core/modules/system/tests/modules/twig_extension_test/templates/twig_extension_test.filter.html.twig
@@ -1,3 +1,6 @@
 <div class="testfilter">
   {{ message|testfilter }}
 </div>
+<div>
+  {{ safe_join_items|safe_join('<br/>') }}
+</div>
diff --git a/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.module b/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.module
index 7e89470..1c2729b 100644
--- a/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.module
+++ b/core/modules/system/tests/modules/twig_extension_test/twig_extension_test.module
@@ -11,7 +11,7 @@
 function twig_extension_test_theme($existing, $type, $theme, $path) {
   return array(
     'twig_extension_test_filter' => array(
-      'variables' => array('message' => NULL),
+      'variables' => array('message' => NULL, 'safe_join_items' => NULL),
       'template' => 'twig_extension_test.filter',
     ),
     'twig_extension_test_function' => array(
diff --git a/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php b/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php
index 1278a6d..7ba686a 100644
--- a/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/SafeMarkupTest.php
@@ -160,7 +160,7 @@ function providerCheckPlain() {
    *
    * @param string $string
    *   The string to run through SafeMarkup::format().
-   * @param string $args
+   * @param string[] $args
    *   The arguments to pass into SafeMarkup::format().
    * @param string $expected
    *   The expected result from calling the function.
@@ -169,10 +169,14 @@ function providerCheckPlain() {
    * @param bool $expected_is_safe
    *   Whether the result is expected to be safe for HTML display.
    */
-  function testFormat($string, $args, $expected, $message, $expected_is_safe) {
+  public function testFormat($string, array $args, $expected, $message, $expected_is_safe) {
     $result = SafeMarkup::format($string, $args);
     $this->assertEquals($expected, $result, $message);
     $this->assertEquals($expected_is_safe, SafeMarkup::isSafe($result), 'SafeMarkup::format correctly sets the result as safe or not safe.');
+
+    foreach ($args as $arg) {
+      $this->assertSame($arg instanceof SafeMarkupTestSafeString, SafeMarkup::isSafe($arg));
+    }
   }
 
   /**
@@ -192,25 +196,6 @@ function providerFormat() {
     return $tests;
   }
 
-  /**
-   * Tests the interaction between the safe list and XSS filtering.
-   *
-   * @covers ::escape
-   */
-  public function testAdminXss() {
-    // Mark the string as safe. This is for test purposes only.
-    $text = '<marquee>text</marquee>';
-    SafeMarkup::set($text);
-
-    // SafeMarkup::escape() will not escape the markup tag since the string was
-    // marked safe above.
-    $this->assertEquals('<marquee>text</marquee>', SafeMarkup::escape($text));
-
-    // SafeMarkup::checkPlain() will escape the markup tag even though the
-    // string was marked safe above.
-    $this->assertEquals('&lt;marquee&gt;text&lt;/marquee&gt;', SafeMarkup::checkPlain($text));
-  }
-
 }
 
 class SafeMarkupTestString {
diff --git a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
index e8718d5..de02997 100644
--- a/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
@@ -7,6 +7,9 @@
 
 namespace Drupal\Tests\Core\Template;
 
+use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Core\Render\RendererInterface;
+use Drupal\Core\Template\TwigEnvironment;
 use Drupal\Core\Template\TwigExtension;
 use Drupal\Tests\UnitTestCase;
 
@@ -124,6 +127,31 @@ public function testSafeStringEscaping() {
     $this->assertSame('&lt;script&gt;alert(&#039;here&#039;);&lt;/script&gt;', $twig_extension->escapeFilter($twig, $string_object, 'html', 'UTF-8', TRUE));
   }
 
+  /**
+   * @covers ::safeJoin
+   */
+  public function testSafeJoin() {
+    $renderer = $this->prophesize(RendererInterface::class);
+    $renderer->render(['#markup' => '<strong>will be rendered</strong>', '#printed' => FALSE])->willReturn('<strong>will be rendered</strong>');
+    $renderer = $renderer->reveal();
+
+    $twig_extension = new TwigExtension($renderer);
+    $twig_environment = $this->prophesize(TwigEnvironment::class)->reveal();
+
+
+    // Simulate t().
+    $string = '<em>will be markup</em>';
+    SafeMarkup::setMultiple([$string => ['html' => TRUE]]);
+
+    $items = [
+      '<em>will be escaped</em>',
+      $string,
+      ['#markup' => '<strong>will be rendered</strong>']
+    ];
+    $result = $twig_extension->safeJoin($twig_environment, $items, '<br/>');
+    $this->assertEquals('&lt;em&gt;will be escaped&lt;/em&gt;<br/><em>will be markup</em><br/><strong>will be rendered</strong>', $result);
+  }
+
 }
 
 class TwigExtensionTestString {
diff --git a/core/themes/engines/twig/twig.engine b/core/themes/engines/twig/twig.engine
index 96d0124..977f094 100644
--- a/core/themes/engines/twig/twig.engine
+++ b/core/themes/engines/twig/twig.engine
@@ -151,29 +151,3 @@ function twig_without($element) {
   }
   return $filtered_element;
 }
-
-/**
- * Overrides twig_join_filter().
- *
- * Safely joins several strings together.
- *
- * @param array|Traversable $value
- *   The pieces to join.
- * @param string $glue
- *   The delimiter with which to join the string. Defaults to an empty string.
- *   This value is expected to be safe for output and user provided data should
- *   never be used as a glue.
- *
- * @return \Twig_Markup
- *   The imploded string, which is wrapped in \Twig_Markup because it is safe.
- */
-function twig_drupal_join_filter($value, $glue = '') {
-  $separator = '';
-  $output = '';
-  foreach ($value as $item) {
-    $output .= $separator . SafeMarkup::escape($item);
-    $separator = $glue;
-  }
-
-  return new \Twig_Markup($output, 'UTF-8');
-}