diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index b24430c37e3b9b8d2ad8d31e07a92d80dc37e8c2..0f6a6c6421fb4539cff35fa9ecc57dd2fa792672 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -13,6 +13,7 @@
 use Drupal\Core\DrupalKernel;
 use Drupal\Core\Extension\ExtensionDiscovery;
 use Drupal\Core\Logger\RfcLogLevel;
+use Drupal\Core\Render\SafeString;
 use Drupal\Core\Session\AccountInterface;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\Utility\Error;
@@ -490,9 +491,9 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
       $_SESSION['messages'][$type] = array();
     }
 
-    // Convert strings which are in the safe markup list to SafeString objects.
-    if (is_string($message) && SafeMarkup::isSafe($message)) {
-      $message = \Drupal\Core\Render\SafeString::create($message);
+    // Convert strings which are safe to the simplest SafeString objects.
+    if (!($message instanceof SafeString) && SafeMarkup::isSafe($message)) {
+      $message = SafeString::create((string) $message);
     }
 
     // Do not use strict type checking so that equivalent string and
diff --git a/core/includes/common.inc b/core/includes/common.inc
index 38a2a3ddbb46a364a81ab14ee80af2503796dc69..ece80d11b591e2a7f03029fd375297323defc897 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -25,6 +25,7 @@
 use Drupal\Core\Render\SafeString;
 use Drupal\Core\Render\Renderer;
 use Drupal\Core\Site\Settings;
+use Drupal\Core\StringTranslation\TranslationWrapper;
 use Drupal\Core\Url;
 use Symfony\Component\HttpFoundation\Response;
 use Symfony\Component\HttpFoundation\Request;
@@ -260,7 +261,7 @@ function check_url($uri) {
  *   Optional language code to translate to a language other than what is used
  *   to display the page.
  *
- * @return
+ * @return \Drupal\Core\StringTranslation\TranslationWrapper
  *   A translated string representation of the size.
  */
 function format_size($size, $langcode = NULL) {
@@ -269,16 +270,7 @@ function format_size($size, $langcode = NULL) {
   }
   else {
     $size = $size / Bytes::KILOBYTE; // Convert bytes to kilobytes.
-    $units = array(
-      t('@size KB', array(), array('langcode' => $langcode)),
-      t('@size MB', array(), array('langcode' => $langcode)),
-      t('@size GB', array(), array('langcode' => $langcode)),
-      t('@size TB', array(), array('langcode' => $langcode)),
-      t('@size PB', array(), array('langcode' => $langcode)),
-      t('@size EB', array(), array('langcode' => $langcode)),
-      t('@size ZB', array(), array('langcode' => $langcode)),
-      t('@size YB', array(), array('langcode' => $langcode)),
-    );
+    $units = ['KB', 'MB', 'GB', 'TB', 'PB', 'EB', 'ZB', 'YB'];
     foreach ($units as $unit) {
       if (round($size, 2) >= Bytes::KILOBYTE) {
         $size = $size / Bytes::KILOBYTE;
@@ -287,7 +279,26 @@ function format_size($size, $langcode = NULL) {
         break;
       }
     }
-    return str_replace('@size', round($size, 2), $unit);
+    $args = ['@size' => round($size, 2)];
+    $options = ['langcode' => $langcode];
+    switch ($unit) {
+      case 'KB':
+        return new TranslationWrapper('@size KB', $args, $options);
+      case 'MB':
+        return new TranslationWrapper('@size MB', $args, $options);
+      case 'GB':
+        return new TranslationWrapper('@size GB', $args, $options);
+      case 'TB':
+        return new TranslationWrapper('@size TB', $args, $options);
+      case 'PB':
+        return new TranslationWrapper('@size PB', $args, $options);
+      case 'EB':
+        return new TranslationWrapper('@size EB', $args, $options);
+      case 'ZB':
+        return new TranslationWrapper('@size ZB', $args, $options);
+      case 'YB':
+        return new TranslationWrapper('@size YB', $args, $options);
+    }
   }
 }
 
diff --git a/core/lib/Drupal/Component/Gettext/PoItem.php b/core/lib/Drupal/Component/Gettext/PoItem.php
index c845c4b07ee431675d03befb06cb776907b9847d..f6737528578833b8765cce9d78344d86507e3b7a 100644
--- a/core/lib/Drupal/Component/Gettext/PoItem.php
+++ b/core/lib/Drupal/Component/Gettext/PoItem.php
@@ -193,7 +193,7 @@ public function setFromArray(array $values = array()) {
         strpos($this->_source, LOCALE_PLURAL_DELIMITER) !== FALSE) {
       $this->setSource(explode(LOCALE_PLURAL_DELIMITER, $this->_source));
       $this->setTranslation(explode(LOCALE_PLURAL_DELIMITER, $this->_translation));
-      $this->setPlural(count($this->_translation) > 1);
+      $this->setPlural(count($this->_source) > 1);
     }
   }
 
diff --git a/core/lib/Drupal/Component/Utility/PlaceholderTrait.php b/core/lib/Drupal/Component/Utility/PlaceholderTrait.php
new file mode 100644
index 0000000000000000000000000000000000000000..0592c377d6128545ec8f8e8648dfa4c169b3817c
--- /dev/null
+++ b/core/lib/Drupal/Component/Utility/PlaceholderTrait.php
@@ -0,0 +1,61 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Component\Utility\PlaceholderTrait.
+ */
+
+namespace Drupal\Component\Utility;
+
+/**
+ * Offers functionality for formatting strings using placeholders.
+ */
+trait PlaceholderTrait {
+
+  /**
+   * Formats a string by replacing variable placeholders.
+   *
+   * @param string $string
+   *   A string containing placeholders.
+   * @param array $args
+   *   An associative array of replacements to make.
+   * @param bool &$safe
+   *   A boolean indicating whether the string is safe or not (optional).
+   *
+   * @return string
+   *   The string with the placeholders replaced.
+   *
+   * @see \Drupal\Component\Utility\SafeMarkup::format()
+   * @see \Drupal\Core\StringTranslation\TranslationWrapper::render()
+   */
+  protected static function placeholderFormat($string, array $args, &$safe = TRUE) {
+    // Transform arguments before inserting them.
+    foreach ($args as $key => $value) {
+      switch ($key[0]) {
+        case '@':
+          // Escaped only.
+          if (!SafeMarkup::isSafe($value)) {
+            $args[$key] = Html::escape($value);
+          }
+          break;
+
+        case '%':
+        default:
+          // Escaped and placeholder.
+          if (!SafeMarkup::isSafe($value)) {
+            $value = Html::escape($value);
+          }
+          $args[$key] = '<em class="placeholder">' . $value . '</em>';
+          break;
+
+        case '!':
+          // Pass-through.
+          if (!SafeMarkup::isSafe($value)) {
+            $safe = FALSE;
+          }
+      }
+    }
+    return strtr($string, $args);
+  }
+
+}
diff --git a/core/lib/Drupal/Component/Utility/SafeMarkup.php b/core/lib/Drupal/Component/Utility/SafeMarkup.php
index 3020bbe5711c3b7fcf85661570db20bf7db8e127..00b09f2574345c1f8d065c175e553d638d1b3214 100644
--- a/core/lib/Drupal/Component/Utility/SafeMarkup.php
+++ b/core/lib/Drupal/Component/Utility/SafeMarkup.php
@@ -31,6 +31,7 @@
  * @see theme_render
  */
 class SafeMarkup {
+  use PlaceholderTrait;
 
   /**
    * The list of safe strings.
@@ -204,40 +205,12 @@ public static function checkPlain($text) {
    */
   public static function format($string, array $args) {
     $safe = TRUE;
-
-    // Transform arguments before inserting them.
-    foreach ($args as $key => $value) {
-      switch ($key[0]) {
-        case '@':
-          // Escaped only.
-          if (!SafeMarkup::isSafe($value)) {
-            $args[$key] = Html::escape($value);
-          }
-          break;
-
-        case '%':
-        default:
-          // Escaped and placeholder.
-          if (!SafeMarkup::isSafe($value)) {
-            $value = Html::escape($value);
-          }
-          $args[$key] = '<em class="placeholder">' . $value . '</em>';
-          break;
-
-        case '!':
-          // Pass-through.
-          if (!static::isSafe($value)) {
-            $safe = FALSE;
-          }
-      }
-    }
-
-    $output = strtr($string, $args);
+    $output = static::placeholderFormat($string, $args, $safe);
     if ($safe) {
       static::$safeStrings[$output]['html'] = TRUE;
     }
-
     return $output;
+
   }
 
 }
diff --git a/core/lib/Drupal/Core/Entity/EntityManager.php b/core/lib/Drupal/Core/Entity/EntityManager.php
index dd3c8f0e62eecea2c878bbd6a15ed694c3c869c1..9d749fbedd78b3a60ebc8bbe3d5bc6697563e8f9 100644
--- a/core/lib/Drupal/Core/Entity/EntityManager.php
+++ b/core/lib/Drupal/Core/Entity/EntityManager.php
@@ -945,9 +945,6 @@ public function getEntityTypeLabels($group = FALSE) {
 
     foreach ($definitions as $entity_type_id => $definition) {
       if ($group) {
-        // We cast the optgroup label to string as array keys must not be
-        // objects and t() may return a TranslationWrapper once issue #2557113
-        // lands.
         $options[(string) $definition->getGroupLabel()][$entity_type_id] = $definition->getLabel();
       }
       else {
@@ -963,8 +960,6 @@ public function getEntityTypeLabels($group = FALSE) {
 
       // Make sure that the 'Content' group is situated at the top.
       $content = $this->t('Content', array(), array('context' => 'Entity type group'));
-      // We cast the optgroup label to string as array keys must not be objects
-      // and t() may return a TranslationWrapper once issue #2557113 lands.
       $options = array((string) $content => $options[(string) $content]) + $options;
     }
 
diff --git a/core/lib/Drupal/Core/StringTranslation/TranslationInterface.php b/core/lib/Drupal/Core/StringTranslation/TranslationInterface.php
index c3e2f68fea52c795b817508253e4b4e57a8f3159..836ad0b2833f7d57d922f64b4c89df83635b93a9 100644
--- a/core/lib/Drupal/Core/StringTranslation/TranslationInterface.php
+++ b/core/lib/Drupal/Core/StringTranslation/TranslationInterface.php
@@ -33,13 +33,24 @@ interface TranslationInterface {
    *      what is used to display the page.
    *   - 'context': The context the source string belongs to.
    *
-   * @return string
+   * @return string|\Drupal\Core\StringTranslation\TranslationWrapper
    *   The translated string.
    *
    * @see \Drupal\Component\Utility\SafeMarkup::format()
    */
   public function translate($string, array $args = array(), array $options = array());
 
+  /**
+   * Translates a TranslationWrapper object to a string.
+   *
+   * @param \Drupal\Core\StringTranslation\TranslationWrapper $translated_string
+   *   A TranslationWrapper object.
+   *
+   * @return string
+   *   The translated string.
+   */
+  public function translateString(TranslationWrapper $translated_string);
+
   /**
    * Formats a string containing a count of items.
    *
diff --git a/core/lib/Drupal/Core/StringTranslation/TranslationManager.php b/core/lib/Drupal/Core/StringTranslation/TranslationManager.php
index af6aa2bc210e97d4294c1c9ebc4d56bd845cfb29..5bf6a9d1eccd925ecf20848560acb7d14996b853 100644
--- a/core/lib/Drupal/Core/StringTranslation/TranslationManager.php
+++ b/core/lib/Drupal/Core/StringTranslation/TranslationManager.php
@@ -140,21 +140,27 @@ public function getStringTranslation($langcode, $string, $context) {
    * {@inheritdoc}
    */
   public function translate($string, array $args = array(), array $options = array()) {
-    $string = $this->doTranslate($string, $options);
-    if (empty($args)) {
-      // We add the string to the safe list as opposed to making it an object
-      // implementing SafeStringInterface as we may need to call __toString()
-      // on the object before render time, at which point the string ceases to
-      // be safe, and working around this would require significant rework.
-      // Adding this string to the safe list is assumed to be safe because
-      // translate() should only be called with strings defined in code.
-      // @see \Drupal\Core\StringTranslation\TranslationInterface::translate()
-      SafeMarkup::setMultiple([$string => ['html' => TRUE]]);
-      return $string;
-    }
-    else {
-      return SafeMarkup::format($string, $args);
+    $safe = TRUE;
+    foreach (array_keys($args) as $arg_key) {
+      // If the string has arguments that start with '!' we consider it unsafe
+      // and return the translation as a string for backward compatibility
+      // purposes.
+      // @todo https://www.drupal.org/node/2570037 remove this temporary
+      // workaround.
+      if (0 === strpos($arg_key, '!') && !SafeMarkup::isSafe($args[$arg_key])) {
+        $safe = FALSE;
+        break;
+      }
     }
+    $wrapper = new TranslationWrapper($string, $args, $options, $this);
+    return $safe ? $wrapper : (string) $wrapper;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function translateString(TranslationWrapper $translated_string) {
+    return $this->doTranslate($translated_string->getUntranslatedString(), $translated_string->getOptions());
   }
 
   /**
@@ -172,13 +178,11 @@ public function translate($string, array $args = array(), array $options = array
    *   The translated string.
    */
   protected function doTranslate($string, array $options = array()) {
-    // Merge in defaults.
-    if (empty($options['langcode'])) {
-      $options['langcode'] = $this->defaultLangcode;
-    }
-    if (empty($options['context'])) {
-      $options['context'] = '';
-    }
+    // Merge in options defaults.
+    $options = $options + [
+      'langcode' => $this->defaultLangcode,
+      'context' => '',
+    ];
     $translation = $this->getStringTranslation($options['langcode'], $string, $options['context']);
     return $translation === FALSE ? $string : $translation;
   }
diff --git a/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php b/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php
index 10e9b12165efd098176857b3ab87490550f0c757..7b4abfc5c59009594fcf4ee6dbbade34b4096e69 100644
--- a/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php
+++ b/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php
@@ -7,21 +7,25 @@
 
 namespace Drupal\Core\StringTranslation;
 
+use Drupal\Component\Utility\PlaceholderTrait;
 use Drupal\Component\Utility\SafeStringInterface;
 use Drupal\Component\Utility\ToStringTrait;
 
 /**
- * Provides a class to wrap a translatable string.
+ * Provides translatable string class.
  *
- * This class can be used to delay translating strings until the translation
- * system is ready. This is useful for using translation in very low level
- * subsystems like entity definition and stream wrappers.
+ * This class delays translating strings until rendering them.
  *
+ * This is useful for using translation in very low level subsystems like entity
+ * definition and stream wrappers.
+ *
+ * @see \Drupal\Core\StringTranslation\TranslationManager::translate()
+ * @see \Drupal\Core\StringTranslation\TranslationManager::translateString()
  * @see \Drupal\Core\Annotation\Translation
  */
 class TranslationWrapper implements SafeStringInterface {
 
-  use StringTranslationTrait;
+  use PlaceholderTrait;
   use ToStringTrait;
 
   /**
@@ -31,6 +35,13 @@ class TranslationWrapper implements SafeStringInterface {
    */
   protected $string;
 
+  /**
+   * The translated string without placeholder replacements.
+   *
+   * @var string
+   */
+  protected $translatedString;
+
   /**
    * The translation arguments.
    *
@@ -45,6 +56,13 @@ class TranslationWrapper implements SafeStringInterface {
    */
   protected $options;
 
+  /**
+   * The string translation service.
+   *
+   * @var \Drupal\Core\StringTranslation\TranslationInterface
+   */
+  protected $stringTranslation;
+
   /**
    * Constructs a new class instance.
    *
@@ -57,11 +75,14 @@ class TranslationWrapper implements SafeStringInterface {
    *   (optional) An array with placeholder replacements, keyed by placeholder.
    * @param array $options
    *   (optional) An array of additional options.
+   * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
+   *   (optional) The string translation service.
    */
-  public function __construct($string, array $arguments = array(), array $options = array()) {
+  public function __construct($string, array $arguments = array(), array $options = array(), TranslationInterface $string_translation = NULL) {
     $this->string = $string;
     $this->arguments = $arguments;
     $this->options = $options;
+    $this->stringTranslation = $string_translation;
   }
 
   /**
@@ -96,6 +117,17 @@ public function getOption($name) {
   public function getOptions() {
     return $this->options;
   }
+
+  /**
+   * Gets all argments from this translation wrapper.
+   *
+   * @return mixed[]
+   *   The array of arguments.
+   */
+  public function getArguments() {
+    return $this->arguments;
+  }
+
   /**
    * Renders the object as a string.
    *
@@ -103,7 +135,18 @@ public function getOptions() {
    *   The translated string.
    */
   public function render() {
-    return $this->t($this->string, $this->arguments, $this->options);
+    if (!isset($this->translatedString)) {
+      $this->translatedString = $this->getStringTranslation()->translateString($this);
+    }
+
+    // Handle any replacements.
+    // @todo https://www.drupal.org/node/2509218 Note that the argument
+    //   replacement is not stored so that different sanitization strategies can
+    //   be used in different contexts.
+    if ($args = $this->getArguments()) {
+      return $this->placeholderFormat($this->translatedString, $args);
+    }
+    return $this->translatedString;
   }
 
   /**
@@ -123,5 +166,18 @@ public function jsonSerialize() {
     return $this->__toString();
   }
 
+  /**
+   * Gets the string translation service.
+   *
+   * @return \Drupal\Core\StringTranslation\TranslationInterface
+   *   The string translation service.
+   */
+  protected function getStringTranslation() {
+    if (!$this->stringTranslation) {
+      $this->stringTranslation = \Drupal::service('string_translation');
+    }
+
+    return $this->stringTranslation;
+  }
 
 }
diff --git a/core/lib/Drupal/Core/Template/Attribute.php b/core/lib/Drupal/Core/Template/Attribute.php
index cc0d591d44543955c08a409c1e488ebaa6ec44c1..76d7c6a52bc4556e6632359e3506989e11033906 100644
--- a/core/lib/Drupal/Core/Template/Attribute.php
+++ b/core/lib/Drupal/Core/Template/Attribute.php
@@ -109,7 +109,8 @@ protected function createAttributeValue($name, $value) {
     elseif (is_bool($value)) {
       $value = new AttributeBoolean($name, $value);
     }
-    elseif (!is_object($value)) {
+    // As a development aid, we allow the value to be a safe string object.
+    elseif (!is_object($value) || $value instanceof SafeStringInterface) {
       $value = new AttributeString($name, $value);
     }
     return $value;
diff --git a/core/lib/Drupal/Core/Validation/DrupalTranslator.php b/core/lib/Drupal/Core/Validation/DrupalTranslator.php
index a2bbf5b580e8359b0d006ee45a4aab349203e8fb..ba1a1f966d57fd47b0a8458385d615ae86d7dc82 100644
--- a/core/lib/Drupal/Core/Validation/DrupalTranslator.php
+++ b/core/lib/Drupal/Core/Validation/DrupalTranslator.php
@@ -7,6 +7,8 @@
 
 namespace Drupal\Core\Validation;
 
+use Drupal\Component\Utility\SafeStringInterface;
+
 /**
  * Translates strings using Drupal's translation system.
  *
@@ -73,8 +75,14 @@ public function getLocale() {
   protected function processParameters(array $parameters) {
     $return = array();
     foreach ($parameters as $key => $value) {
+      // We allow the values in the parameters to be safe string objects. This
+      // can be useful when we want to use parameter values that are
+      // TranslationWrappers.
+      if ($value instanceof SafeStringInterface) {
+        $value = (string) $value;
+      }
       if (is_object($value)) {
-        // t() does not work will objects being passed as replacement strings.
+        // t() does not work with objects being passed as replacement strings.
       }
       // Check for symfony replacement patterns in the form "{{ name }}".
       elseif (strpos($key, '{{ ') === 0 && strrpos($key, ' }}') == strlen($key) - 3) {
diff --git a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
index d873820b28edeb612b5c6958d9b3ab1fde63c337..6fa8771dd39d1a02661c6e423c853ccbd7f0cca0 100644
--- a/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
+++ b/core/lib/Drupal/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidator.php
@@ -16,6 +16,7 @@
 use Drupal\Core\TypedData\Type\StringInterface;
 use Drupal\Core\TypedData\Type\UriInterface;
 use Drupal\Core\TypedData\Validation\TypedDataAwareValidatorTrait;
+use Drupal\Component\Utility\SafeStringInterface;
 use Symfony\Component\Validator\Constraint;
 use Symfony\Component\Validator\ConstraintValidator;
 
@@ -49,7 +50,7 @@ public function validate($value, Constraint $constraint) {
     if ($typed_data instanceof IntegerInterface && filter_var($value, FILTER_VALIDATE_INT) === FALSE) {
       $valid = FALSE;
     }
-    if ($typed_data instanceof StringInterface && !is_scalar($value)) {
+    if ($typed_data instanceof StringInterface && !is_scalar($value) && !($value instanceof SafeStringInterface)) {
       $valid = FALSE;
     }
     // Ensure that URIs comply with http://tools.ietf.org/html/rfc3986, which
diff --git a/core/modules/ckeditor/ckeditor.admin.inc b/core/modules/ckeditor/ckeditor.admin.inc
index d5bb6906f7a110d326dae73b9467bd80cebe57e4..912076314e0512fc794ed731c489d0fca1f6e309 100644
--- a/core/modules/ckeditor/ckeditor.admin.inc
+++ b/core/modules/ckeditor/ckeditor.admin.inc
@@ -117,8 +117,6 @@ function template_preprocess_ckeditor_settings_toolbar(&$variables) {
   $variables['active_buttons'] = array();
   foreach ($active_buttons as $row_number => $button_row) {
     foreach ($button_groups[$row_number] as $group_name) {
-      // We cast the group name to string as array keys must not be objects
-      // and t() may return a TranslationWrapper once issue #2557113 lands.
       $group_name = (string) $group_name;
       $variables['active_buttons'][$row_number][$group_name] = array(
         'group_name_class' => Html::getClass($group_name),
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index 9240ce6ef36f66c40b2ac4a24b736e127ea1ff96..0756a5333b70f1d3cb38a73c94fafa71c1dff606 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -298,8 +298,6 @@ function comment_form_field_ui_field_storage_add_form_alter(&$form, FormStateInt
     $form['#title'] = \Drupal::service('comment.manager')->getFieldUIPageTitle($route_match->getParameter('commented_entity_type'), $route_match->getParameter('field_name'));
   }
   if (!_comment_entity_uses_integer_id($form_state->get('entity_type_id'))) {
-    // We cast the optgroup label to string as array keys must not be objects
-    // and t() will return a TranslationWrapper once issue #2557113 lands.
     $optgroup = (string) t('General');
     // You cannot use comment fields on entity types with non-integer IDs.
     unset($form['add']['new_storage_type']['#options'][$optgroup]['comment']);
diff --git a/core/modules/entity_reference/entity_reference.module b/core/modules/entity_reference/entity_reference.module
index 908e0e58de9bbfc03adaf1b2ada9e803047c0d78..ae4cc039c1046e101ccb703ddd916142164bca85 100644
--- a/core/modules/entity_reference/entity_reference.module
+++ b/core/modules/entity_reference/entity_reference.module
@@ -126,8 +126,6 @@ function entity_reference_field_config_presave(FieldConfigInterface $field) {
  * Implements hook_form_FORM_ID_alter() for 'field_ui_field_storage_add_form'.
  */
 function entity_reference_form_field_ui_field_storage_add_form_alter(array &$form) {
-  // We cast the optgroup label to string as array keys must not be objects
-  // and t() may return a TranslationWrapper once issue #2557113 lands.
   $optgroup = (string) t('Reference');
   // Move the "Entity reference" option to the end of the list and rename it to
   // "Other".
diff --git a/core/modules/language/src/Form/NegotiationBrowserForm.php b/core/modules/language/src/Form/NegotiationBrowserForm.php
index 111f35af5dfde134a02d7ff0cbdb1b30a8ccf112..5fa186a7ba58bd2d64e5f3fe5204c51dc63d75fd 100644
--- a/core/modules/language/src/Form/NegotiationBrowserForm.php
+++ b/core/modules/language/src/Form/NegotiationBrowserForm.php
@@ -82,8 +82,6 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     }
     else {
       $language_options = array(
-        // We cast the optgroup labels to string as array keys must not be objects
-        // and t() may return a TranslationWrapper once issue #2557113 lands.
         (string) $this->t('Existing languages') => $existing_languages,
         (string) $this->t('Languages not yet added') => $this->languageManager->getStandardLanguageListWithoutConfigured(),
       );
diff --git a/core/modules/locale/locale.module b/core/modules/locale/locale.module
index 80620a088583aff4f55f92ee2b95dd910ba11e2c..7259d35b1dba8483957a40152a25800b16e15249 100644
--- a/core/modules/locale/locale.module
+++ b/core/modules/locale/locale.module
@@ -641,7 +641,7 @@ function locale_form_language_admin_overview_form_alter(&$form, FormStateInterfa
     }
   }
 
-  array_splice($form['languages']['#header'], -1, 0, t('Interface translation'));
+  array_splice($form['languages']['#header'], -1, 0, ['translation-interface' => t('Interface translation')]);
 
   foreach ($languages as $langcode => $language) {
     $stats[$langcode] += array(
diff --git a/core/modules/locale/src/Form/ImportForm.php b/core/modules/locale/src/Form/ImportForm.php
index 86aecc34921e296fe9e41288e8c8254fb0a9f5e9..f3007f63e8391bbe91408ade4f1472f5486e62cd 100644
--- a/core/modules/locale/src/Form/ImportForm.php
+++ b/core/modules/locale/src/Form/ImportForm.php
@@ -94,8 +94,6 @@ public function buildForm(array $form, FormStateInterface $form_state) {
     else {
       $default = key($existing_languages);
       $language_options = array(
-        // We cast the optgroup labels to string as array keys must not be objects
-        // and t() may return a TranslationWrapper once issue #2557113 lands.
         (string) $this->t('Existing languages') => $existing_languages,
         (string) $this->t('Languages not yet added') => $this->languageManager->getStandardLanguageListWithoutConfigured(),
       );
diff --git a/core/modules/locale/src/Tests/LocaleTranslationUiTest.php b/core/modules/locale/src/Tests/LocaleTranslationUiTest.php
index 6c35b1800f24169f1100296ef429de6bbee01f66..a6999b842433ea1aca17fa2975dda2ca84121862 100644
--- a/core/modules/locale/src/Tests/LocaleTranslationUiTest.php
+++ b/core/modules/locale/src/Tests/LocaleTranslationUiTest.php
@@ -64,7 +64,7 @@ public function testStringTranslation() {
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
     // Add string.
-    t($name, array(), array('langcode' => $langcode));
+    t($name, array(), array('langcode' => $langcode))->render();
     // Reset locale cache.
     $this->container->get('string_translation')->reset();
     $this->assertRaw('"edit-languages-' . $langcode . '-weight"', 'Language code found.');
@@ -237,9 +237,10 @@ public function testJavaScriptTranslation() {
 
     // Retrieve the source string of the first string available in the
     // {locales_source} table and translate it.
-    $source = db_select('locales_source', 'l')
-      ->fields('l', array('source'))
-      ->condition('l.source', '%.js%', 'LIKE')
+    $query = db_select('locales_source', 's');
+    $query->addJoin('INNER', 'locales_location', 'l', 's.lid = l.lid');
+    $source = $query->fields('s', array('source'))
+      ->condition('l.type', 'javascript')
       ->range(0, 1)
       ->execute()
       ->fetchField();
@@ -302,7 +303,7 @@ public function testStringValidation() {
     );
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
     // Add string.
-    t($name, array(), array('langcode' => $langcode));
+    t($name, array(), array('langcode' => $langcode))->render();
     // Reset locale cache.
     $search = array(
       'string' => $name,
@@ -361,7 +362,7 @@ public function testStringSearch() {
     $this->drupalPostForm('admin/config/regional/language/add', $edit, t('Add custom language'));
 
     // Add string.
-    t($name, array(), array('langcode' => $langcode));
+    t($name, array(), array('langcode' => $langcode))->render();
     // Reset locale cache.
     $this->container->get('string_translation')->reset();
     $this->drupalLogout();
diff --git a/core/modules/simpletest/src/AssertContentTrait.php b/core/modules/simpletest/src/AssertContentTrait.php
index eb1a80c66119e1470c091d8ac261b793b98e07d4..9ef0a662bb8d479091555970bca86108944cdae3 100644
--- a/core/modules/simpletest/src/AssertContentTrait.php
+++ b/core/modules/simpletest/src/AssertContentTrait.php
@@ -806,6 +806,8 @@ protected function assertTitle($title, $message = '', $group = 'Other') {
     preg_match('@<title>(.*)</title>@', $this->getRawContent(), $matches);
     if (isset($matches[1])) {
       $actual = $matches[1];
+      $actual = $this->castSafeStrings($actual);
+      $title = $this->castSafeStrings($title);
       if (!$message) {
         $message = SafeMarkup::format('Page title @actual is equal to @expected.', array(
           '@actual' => var_export($actual, TRUE),
diff --git a/core/modules/system/src/Tests/File/NameMungingTest.php b/core/modules/system/src/Tests/File/NameMungingTest.php
index 10caf61bf89d432cd774f1be54e4c6ae9f52ab56..3afd2735d5cdc2dd91f8c0ec32dc68da1ae84e69 100644
--- a/core/modules/system/src/Tests/File/NameMungingTest.php
+++ b/core/modules/system/src/Tests/File/NameMungingTest.php
@@ -44,7 +44,7 @@ function testMunging() {
     $this->config('system.file')->set('allow_insecure_uploads', 0)->save();
     $munged_name = file_munge_filename($this->name, '', TRUE);
     $messages = drupal_get_messages();
-    $this->assertTrue(in_array(t('For security reasons, your upload has been renamed to %filename.', array('%filename' => $munged_name)), $messages['status']), 'Alert properly set when a file is renamed.');
+    $this->assertTrue(in_array(strtr('For security reasons, your upload has been renamed to <em class="placeholder">%filename</em>.', array('%filename' => $munged_name)), $messages['status']), 'Alert properly set when a file is renamed.');
     $this->assertNotEqual($munged_name, $this->name, format_string('The new filename (%munged) has been modified from the original (%original)', array('%munged' => $munged_name, '%original' => $this->name)));
   }
 
diff --git a/core/modules/system/src/Tests/Form/FormTest.php b/core/modules/system/src/Tests/Form/FormTest.php
index 83b9129014a51f353e3bf172f9a5604257d71dac..389d23efe27fa647d338cc400bd9b6c19aadec85 100644
--- a/core/modules/system/src/Tests/Form/FormTest.php
+++ b/core/modules/system/src/Tests/Form/FormTest.php
@@ -144,7 +144,7 @@ function testRequiredFields() {
               // Select elements are going to have validation errors with empty
               // input, since those are illegal choices. Just make sure the
               // error is not "field is required".
-              $this->assertTrue((empty($errors[$element]) || strpos('field is required', $errors[$element]) === FALSE), "Optional '$type' field '$element' is not treated as a required element");
+              $this->assertTrue((empty($errors[$element]) || strpos('field is required', (string) $errors[$element]) === FALSE), "Optional '$type' field '$element' is not treated as a required element");
             }
             else {
               // Make sure there is *no* form error for this element.
diff --git a/core/modules/system/tests/modules/plugin_test/src/Plugin/MockBlockManager.php b/core/modules/system/tests/modules/plugin_test/src/Plugin/MockBlockManager.php
index e435c0a22973903bc7e63c9a9eea5548b5b96902..f079785741d047b54af62652a2e842728855560a 100644
--- a/core/modules/system/tests/modules/plugin_test/src/Plugin/MockBlockManager.php
+++ b/core/modules/system/tests/modules/plugin_test/src/Plugin/MockBlockManager.php
@@ -78,7 +78,7 @@ public function __construct() {
       'label' => t('User name'),
       'class' => 'Drupal\plugin_test\Plugin\plugin_test\mock_block\MockUserNameBlock',
       'context' => array(
-        'user' => new ContextDefinition('entity:user', t('User')),
+        'user' => $this->createContextDefinition('entity:user', t('User')),
       ),
     ));
 
@@ -87,7 +87,7 @@ public function __construct() {
       'label' => t('User name optional'),
       'class' => 'Drupal\plugin_test\Plugin\plugin_test\mock_block\MockUserNameBlock',
       'context' => array(
-        'user' => new ContextDefinition('entity:user', t('User'), FALSE),
+        'user' => $this->createContextDefinition('entity:user', t('User'), FALSE),
       ),
     ));
 
@@ -102,8 +102,8 @@ public function __construct() {
       'label' => t('Complex context'),
       'class' => 'Drupal\plugin_test\Plugin\plugin_test\mock_block\MockComplexContextBlock',
       'context' => array(
-        'user' => new ContextDefinition('entity:user', t('User')),
-        'node' => new ContextDefinition('entity:node', t('Node')),
+        'user' => $this->createContextDefinition('entity:user', t('User')),
+        'node' => $this->createContextDefinition('entity:node', t('Node')),
       ),
     ));
 
@@ -118,4 +118,24 @@ public function __construct() {
     // specified), so we provide it the discovery object.
     $this->factory = new ReflectionFactory($this->discovery);
   }
+
+  /**
+   * Creates a new context definition with a label that is cast to string.
+   *
+   * @param string $data_type
+   *   The required data type.
+   * @param mixed string|null $label
+   *   The label of this context definition for the UI.
+   * @param bool $required
+   *   Whether the context definition is required.
+   *
+   * @return \Drupal\Core\Plugin\Context\ContextDefinition
+   */
+  protected function createContextDefinition($data_type, $label, $required = TRUE) {
+    // We cast the label to string for testing purposes only, as it may be
+    // a TranslationWrapper and we will do assertEqual() checks on arrays that
+    // include ContextDefinition objects, and var_export() has problems
+    // printing TranslationWrapper objects.
+    return new ContextDefinition($data_type, (string) $label, $required);
+  }
 }
diff --git a/core/modules/update/update.module b/core/modules/update/update.module
index 63a76b6b2e4dcc97aa1de6418e4386d9d99391d7..6f94d219a18db5230977307482c3cfd925f4aa05 100644
--- a/core/modules/update/update.module
+++ b/core/modules/update/update.module
@@ -140,6 +140,11 @@ function update_page_top() {
     $status = update_requirements('runtime');
     foreach (array('core', 'contrib') as $report_type) {
       $type = 'update_' . $report_type;
+      // hook_requirements() supports render arrays therefore we need to render
+      // them before using drupal_set_message().
+      if (isset($status[$type]['description']) && is_array($status[$type]['description'])) {
+        $status[$type]['description'] = \Drupal::service('renderer')->renderPlain($status[$type]['description']);
+      }
       if (!empty($verbose)) {
         if (isset($status[$type]['severity'])) {
           if ($status[$type]['severity'] == REQUIREMENT_ERROR) {
diff --git a/core/modules/user/src/Tests/UserCancelTest.php b/core/modules/user/src/Tests/UserCancelTest.php
index 535701340972c9fd7e66e1eaf8ea38cf5a556892..648f56ff57035dafacea5c15b5c139453301fe8c 100644
--- a/core/modules/user/src/Tests/UserCancelTest.php
+++ b/core/modules/user/src/Tests/UserCancelTest.php
@@ -535,7 +535,7 @@ function testMassUserCancelByAdmin() {
     $this->drupalPostForm(NULL, NULL, t('Cancel accounts'));
     $status = TRUE;
     foreach ($users as $account) {
-      $status = $status && (strpos($this->content, t('%name has been deleted.', array('%name' => $account->getUsername()))) !== FALSE);
+      $status = $status && (strpos($this->content,  $account->getUsername() . '</em> has been deleted.') !== FALSE);
       $user_storage->resetCache(array($account->id()));
       $status = $status && !$user_storage->load($account->id());
     }
diff --git a/core/modules/views/src/Plugin/views/PluginBase.php b/core/modules/views/src/Plugin/views/PluginBase.php
index b8b7a30ed8286b354c66618ea843c3986792b0ba..cbe75261f39ffe5b565d532cec17347a3af271c5 100644
--- a/core/modules/views/src/Plugin/views/PluginBase.php
+++ b/core/modules/views/src/Plugin/views/PluginBase.php
@@ -14,6 +14,7 @@
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\Core\Plugin\PluginBase as ComponentPluginBase;
 use Drupal\Core\Render\Element;
+use Drupal\Core\StringTranslation\TranslationWrapper;
 use Drupal\views\Plugin\views\display\DisplayPluginBase;
 use Drupal\views\ViewExecutable;
 use Symfony\Component\DependencyInjection\ContainerInterface;
@@ -561,7 +562,14 @@ protected function listLanguages($flags = LanguageInterface::STATE_ALL, array $c
     // Since this is not a real language, surround it by '***LANGUAGE_...***',
     // like the negotiated languages below.
     if ($flags & LanguageInterface::STATE_SITE_DEFAULT) {
-      $list[PluginBase::VIEWS_QUERY_LANGUAGE_SITE_DEFAULT] = $this->t($languages[LanguageInterface::LANGCODE_SITE_DEFAULT]->getName());
+      $name = $languages[LanguageInterface::LANGCODE_SITE_DEFAULT]->getName();
+      // The language name may have already been translated, no need to
+      // translate it again.
+      // @see Drupal\Core\Language::filterLanguages().
+      if (!$name instanceof TranslationWrapper) {
+        $name = $this->t($name);
+      }
+      $list[PluginBase::VIEWS_QUERY_LANGUAGE_SITE_DEFAULT] = $name;
       // Remove site default language from $languages so it's not added
       // twice with the real languages below.
       unset($languages[LanguageInterface::LANGCODE_SITE_DEFAULT]);
diff --git a/core/modules/views/src/Plugin/views/area/TokenizeAreaPluginBase.php b/core/modules/views/src/Plugin/views/area/TokenizeAreaPluginBase.php
index 2e4564e5da008546dd6aff919bd8de65a3050f07..1a97ee5191f52291aa635a6e10390899072581d8 100644
--- a/core/modules/views/src/Plugin/views/area/TokenizeAreaPluginBase.php
+++ b/core/modules/views/src/Plugin/views/area/TokenizeAreaPluginBase.php
@@ -52,8 +52,6 @@ public function tokenForm(&$form, FormStateInterface $form_state) {
 
     // Get a list of the available fields and arguments for token replacement.
     $options = array();
-    // We cast the optgroup labels to string as array keys must not be objects
-    // and t() may return a TranslationWrapper once issue #2557113 lands.
     $optgroup_arguments = (string) t('Arguments');
     $optgroup_fields = (string) t('Fields');
     foreach ($this->view->display_handler->getHandlers('field') as $field => $handler) {
diff --git a/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php b/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php
index 1bb339440a6ba0ab987478a37d0ab04c0d11b984..76ae608b1add19cd3c8eba7069dcb625ae032dcc 100644
--- a/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php
+++ b/core/modules/views/src/Plugin/views/display/DisplayPluginBase.php
@@ -1725,9 +1725,6 @@ public function buildOptionsForm(&$form, FormStateInterface $form_state) {
         );
 
         $options = array();
-        // We cast the optgroup label to string as array keys must not be
-        // objects and t() may return a TranslationWrapper once issue #2557113
-        // lands.
         $optgroup_arguments = (string) t('Arguments');
         foreach ($this->view->display_handler->getHandlers('argument') as $arg => $handler) {
           $options[$optgroup_arguments]["{{ arguments.$arg }}"] = $this->t('@argument title', array('@argument' => $handler->adminLabel()));
diff --git a/core/modules/views/src/Plugin/views/field/FieldPluginBase.php b/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
index 29abf887c3008064ff47bbd1f5e04246df3a8328..bfdd1a021fb4fb2e639daff00a2426c05de1969b 100644
--- a/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
+++ b/core/modules/views/src/Plugin/views/field/FieldPluginBase.php
@@ -862,8 +862,6 @@ public function buildOptionsForm(&$form, FormStateInterface $form_state) {
 
       // Setup the tokens for fields.
       $previous = $this->getPreviousFieldLabels();
-      // We cast the optgroup labels to string as array keys must not be objects
-      // and t() may return a TranslationWrapper once issue #2557113 lands.
       $optgroup_arguments = (string) t('Arguments');
       $optgroup_fields = (string) t('Fields');
       foreach ($previous as $id => $label) {
diff --git a/core/tests/Drupal/KernelTests/Core/Common/DrupalSetMessageTest.php b/core/tests/Drupal/KernelTests/Core/Common/DrupalSetMessageTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..3ef61629274ad404bad2dd80e0b403159e2bbd6a
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/Core/Common/DrupalSetMessageTest.php
@@ -0,0 +1,34 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\KernelTests\Core\Common\DrupalSetMessageTest.
+ */
+
+namespace Drupal\KernelTests\Core\Common;
+
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * @covers ::drupal_set_message
+ * @group PHPUnit
+ */
+class DrupalSetMessageTest extends KernelTestBase {
+
+  /**
+   * The basic functionality of drupal_set_message().
+   */
+  public function testDrupalSetMessage() {
+    drupal_set_message(t('A message: @foo', ['@foo' => 'bar']));
+    $messages = drupal_get_messages();
+    $this->assertInstanceOf('Drupal\Core\Render\SafeString', $messages['status'][0]);
+    $this->assertEquals('A message: bar', (string) $messages['status'][0]);
+  }
+
+  public function tearDown() {
+    // Clear session to prevent global leakage.
+    unset($_SESSION['messages']);
+    parent::tearDown();
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/Core/Annotation/TranslationTest.php b/core/tests/Drupal/Tests/Core/Annotation/TranslationTest.php
index be8cca3b8495f1044a5b37f78fb41259e913ca2b..f06254c2abbe6601d316f8f43a8ad234f4cc50eb 100644
--- a/core/tests/Drupal/Tests/Core/Annotation/TranslationTest.php
+++ b/core/tests/Drupal/Tests/Core/Annotation/TranslationTest.php
@@ -45,9 +45,6 @@ public function testGet(array $values, $expected) {
     $options = isset($values['context']) ? array(
       'context' => $values['context'],
     ) : array();
-    $this->translationManager->expects($this->once())
-      ->method('translate')
-      ->with($values['value'], $arguments, $options);
 
     $annotation = new Translation($values);
 
diff --git a/core/tests/Drupal/Tests/Core/Menu/ContextualLinkDefaultTest.php b/core/tests/Drupal/Tests/Core/Menu/ContextualLinkDefaultTest.php
index ac920882544500c1b88be9cd70254e89b7692a55..15991a563fefca6bd1ebf26fd3d710b9dc18e125 100644
--- a/core/tests/Drupal/Tests/Core/Menu/ContextualLinkDefaultTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/ContextualLinkDefaultTest.php
@@ -71,11 +71,10 @@ protected function setupContextualLinkDefault() {
    */
   public function testGetTitle() {
     $title = 'Example';
-    $this->pluginDefinition['title'] = (new TranslationWrapper($title))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper($title, [], [], $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with($title, array(), array())
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example translated'));
 
     $this->setupContextualLinkDefault();
@@ -87,11 +86,10 @@ public function testGetTitle() {
    */
   public function testGetTitleWithContext() {
     $title = 'Example';
-    $this->pluginDefinition['title'] = (new TranslationWrapper($title, array(), array('context' => 'context')))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper($title, array(), array('context' => 'context'), $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with($title, array(), array('context' => 'context'))
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example translated with context'));
 
     $this->setupContextualLinkDefault();
@@ -103,11 +101,10 @@ public function testGetTitleWithContext() {
    */
   public function testGetTitleWithTitleArguments() {
     $title = 'Example @test';
-    $this->pluginDefinition['title'] = (new TranslationWrapper($title, array('@test' => 'value')))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper($title, array('@test' => 'value'), [], $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with($title, array('@test' => 'value'), array())
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example value'));
 
     $this->setupContextualLinkDefault();
diff --git a/core/tests/Drupal/Tests/Core/Menu/LocalActionDefaultTest.php b/core/tests/Drupal/Tests/Core/Menu/LocalActionDefaultTest.php
index 02d4578d44953e51484b262e0f70b993f841148a..3de7774a838633e978e663b779c16698cbb1a95b 100644
--- a/core/tests/Drupal/Tests/Core/Menu/LocalActionDefaultTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/LocalActionDefaultTest.php
@@ -83,11 +83,10 @@ protected function setupLocalActionDefault() {
    * @see \Drupal\Core\Menu\LocalTaskDefault::getTitle()
    */
   public function testGetTitle() {
-    $this->pluginDefinition['title'] = (new TranslationWrapper('Example'))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper('Example', [], [], $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with('Example', array(), array())
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example translated'));
 
     $this->setupLocalActionDefault();
@@ -100,11 +99,10 @@ public function testGetTitle() {
    * @see \Drupal\Core\Menu\LocalTaskDefault::getTitle()
    */
   public function testGetTitleWithContext() {
-    $this->pluginDefinition['title'] = (new TranslationWrapper('Example', array(), array('context' => 'context')))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper('Example', array(), array('context' => 'context'), $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with('Example', array(), array('context' => 'context'))
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example translated with context'));
 
     $this->setupLocalActionDefault();
@@ -115,11 +113,10 @@ public function testGetTitleWithContext() {
    * Tests the getTitle method with title arguments.
    */
   public function testGetTitleWithTitleArguments() {
-    $this->pluginDefinition['title'] = (new TranslationWrapper('Example @test', array('@test' => 'value')))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper('Example @test', array('@test' => 'value'), [], $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with('Example @test', array('@test' => 'value'), array())
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example value'));
 
     $this->setupLocalActionDefault();
diff --git a/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php b/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php
index d4032eccc2334f7e09c607c08dbc24a7c2d3a711..7c9dc58ed614a4e2da0843eb733a329d5f93b3cf 100644
--- a/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php
@@ -233,11 +233,10 @@ public function testActive() {
    * @covers ::getTitle
    */
   public function testGetTitle() {
-    $this->pluginDefinition['title'] = (new TranslationWrapper('Example'))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper('Example', [], [], $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with('Example', array(), array())
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example translated'));
 
     $this->setupLocalTaskDefault();
@@ -249,11 +248,10 @@ public function testGetTitle() {
    */
   public function testGetTitleWithContext() {
     $title = 'Example';
-    $this->pluginDefinition['title'] = (new TranslationWrapper($title, array(), array('context' => 'context')))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper($title, array(), array('context' => 'context'), $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with($title, array(), array('context' => 'context'))
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example translated with context'));
 
     $this->setupLocalTaskDefault();
@@ -264,12 +262,10 @@ public function testGetTitleWithContext() {
    * @covers ::getTitle
    */
   public function testGetTitleWithTitleArguments() {
-    $title = 'Example @test';
-    $this->pluginDefinition['title'] = (new TranslationWrapper('Example @test', array('@test' => 'value')))
-      ->setStringTranslation($this->stringTranslation);
+    $this->pluginDefinition['title'] = (new TranslationWrapper('Example @test', array('@test' => 'value'), [], $this->stringTranslation));
     $this->stringTranslation->expects($this->once())
-      ->method('translate')
-      ->with($title, array('@test' => 'value'), array())
+      ->method('translateString')
+      ->with($this->pluginDefinition['title'])
       ->will($this->returnValue('Example value'));
 
     $this->setupLocalTaskDefault();
diff --git a/core/tests/Drupal/Tests/Core/StringTranslation/TranslationManagerTest.php b/core/tests/Drupal/Tests/Core/StringTranslation/TranslationManagerTest.php
index 53165c97c902d40a8da947f87152919b2b8f1a94..4efd7010f4f737675a3a53b5a606f066edcb9e85 100644
--- a/core/tests/Drupal/Tests/Core/StringTranslation/TranslationManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/StringTranslation/TranslationManagerTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\Tests\Core\StringTranslation {
 
 use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Component\Utility\SafeStringInterface;
 use Drupal\Core\StringTranslation\TranslationManager;
 use Drupal\Tests\UnitTestCase;
 
@@ -59,6 +60,44 @@ public function testFormatPlural($count, $singular, $plural, array $args = array
     $this->assertEquals(SafeMarkup::isSafe($result), $safe);
   }
 
+  /**
+   * Tests translation using placeholders.
+   *
+   * @param string $string
+   *   A string containing the English string to translate.
+   * @param array $args
+   *   An associative array of replacements to make after translation.
+   * @param string $expected_string
+   *   The expected translated string value.
+   * @param bool $returns_translation_wrapper
+   *   Whether we are expecting a TranslationWrapper object to be returned.
+   *
+   * @dataProvider providerTestTranslatePlaceholder
+   */
+  public function testTranslatePlaceholder($string, array $args = array(), $expected_string, $returns_translation_wrapper) {
+    $actual = $this->translationManager->translate($string, $args);
+    if ($returns_translation_wrapper) {
+      $this->assertInstanceOf(SafeStringInterface::class, $actual);
+    }
+    else {
+      $this->assertInternalType('string', $actual);
+    }
+    $this->assertEquals($expected_string, $actual);
+  }
+
+  /**
+   * Provides test data for translate().
+   *
+   * @return array
+   */
+  public function providerTestTranslatePlaceholder() {
+    return [
+      ['foo @bar', ['@bar' => 'bar'], 'foo bar', TRUE],
+      ['bar !baz', ['!baz' => 'baz'], 'bar baz', FALSE],
+      ['bar @bar !baz', ['@bar' => 'bar', '!baz' => 'baz'], 'bar bar baz', FALSE],
+      ['bar !baz @bar', ['!baz' => 'baz', '@bar' => 'bar'], 'bar baz bar', FALSE],
+    ];
+  }
 }
 
 class TestTranslationManager extends TranslationManager {
diff --git a/core/tests/Drupal/Tests/Core/StringTranslation/TranslationWrapperTest.php b/core/tests/Drupal/Tests/Core/StringTranslation/TranslationWrapperTest.php
index 3facf382e4315d59c9d897154ee34740c95fb7fb..af5dce8c03ea7cd145628ea04acf3193e1003c0e 100644
--- a/core/tests/Drupal/Tests/Core/StringTranslation/TranslationWrapperTest.php
+++ b/core/tests/Drupal/Tests/Core/StringTranslation/TranslationWrapperTest.php
@@ -8,6 +8,7 @@
 namespace Drupal\Tests\Core\StringTranslation;
 
 use Drupal\Core\StringTranslation\TranslationInterface;
+use Drupal\Core\StringTranslation\TranslationWrapper;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -55,9 +56,11 @@ public function errorHandler($error_number, $error_message) {
    * @covers ::__toString
    */
   public function testToString() {
+    $translation = $this->getMock(TranslationInterface::class);
+
     $string = 'May I have an exception please?';
-    $text = $this->getMockBuilder('Drupal\Core\StringTranslation\TranslationWrapper')
-      ->setConstructorArgs([$string])
+    $text = $this->getMockBuilder(TranslationWrapper::class)
+      ->setConstructorArgs([$string, [], [], $translation])
       ->setMethods(['_die'])
       ->getMock();
     $text
@@ -65,11 +68,12 @@ public function testToString() {
       ->method('_die')
       ->willReturn('');
 
-    $translation = $this->prophesize(TranslationInterface::class);
-    $translation->translate($string, [], [])->will(function () {
+    $translation
+      ->method('translateString')
+      ->with($text)
+      ->willReturnCallback(function () {
       throw new \Exception('Yes you may.');
     });
-    $text->setStringTranslation($translation->reveal());
 
     // We set a custom error handler because of https://github.com/sebastianbergmann/phpunit/issues/487
     set_error_handler([$this, 'errorHandler']);
diff --git a/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php b/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php
index 2bcb3185f65015d5b2cfbc70aa8286ba9f140c8e..0707fa3baf3c8285537f38cd225196bd73f7c8c7 100644
--- a/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php
+++ b/core/tests/Drupal/Tests/Core/Validation/Plugin/Validation/Constraint/PrimitiveTypeConstraintValidatorTest.php
@@ -16,6 +16,7 @@
 use Drupal\Core\TypedData\PrimitiveInterface;
 use Drupal\Core\Validation\Plugin\Validation\Constraint\PrimitiveTypeConstraint;
 use Drupal\Core\Validation\Plugin\Validation\Constraint\PrimitiveTypeConstraintValidator;
+use Drupal\Core\StringTranslation\TranslationWrapper;
 use Drupal\Tests\UnitTestCase;
 
 /**
@@ -63,6 +64,7 @@ public function provideTestValidate() {
     $data[] = [new IntegerData(DataDefinition::create('integer')), 1.5, FALSE];
     $data[] = [new IntegerData(DataDefinition::create('integer')), 'test', FALSE];
     $data[] = [new StringData(DataDefinition::create('string')), 'test', TRUE];
+    $data[] = [new StringData(DataDefinition::create('string')), new TranslationWrapper('test'), TRUE];
     // It is odd that 1 is a valid string.
     // $data[] = [$this->getMock('Drupal\Core\TypedData\Type\StringInterface'), 1, FALSE];
     $data[] = [new StringData(DataDefinition::create('string')), [], FALSE];
diff --git a/core/tests/Drupal/Tests/UnitTestCase.php b/core/tests/Drupal/Tests/UnitTestCase.php
index 3433c942c00585e7c986e766ae724ca69983fdd8..e327a84be6fb30e681d3f06403cd88a4089555f8 100644
--- a/core/tests/Drupal/Tests/UnitTestCase.php
+++ b/core/tests/Drupal/Tests/UnitTestCase.php
@@ -12,6 +12,8 @@
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Cache\CacheTagsInvalidatorInterface;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Component\Utility\PlaceholderTrait;
+use Drupal\Core\StringTranslation\TranslationWrapper;
 
 /**
  * Provides a base class and helpers for Drupal unit tests.
@@ -20,6 +22,8 @@
  */
 abstract class UnitTestCase extends \PHPUnit_Framework_TestCase {
 
+  use PlaceholderTrait;
+
   /**
    * The random generator.
    *
@@ -214,7 +218,17 @@ public function getStringTranslationStub() {
     $translation = $this->getMock('Drupal\Core\StringTranslation\TranslationInterface');
     $translation->expects($this->any())
       ->method('translate')
-      ->will($this->returnCallback('Drupal\Component\Utility\SafeMarkup::format'));
+      ->willReturnCallback(function ($string, array $args = array(), array $options = array()) use ($translation) {
+        $wrapper = new TranslationWrapper($string, $args, $options, $translation);
+        // Pretend everything is not safe.
+        // @todo https://www.drupal.org/node/2570037 return the wrapper instead.
+        return (string) $wrapper;
+      });
+    $translation->expects($this->any())
+      ->method('translateString')
+      ->willReturnCallback(function (TranslationWrapper $wrapper) {
+        return $wrapper->getUntranslatedString();
+      });
     $translation->expects($this->any())
       ->method('formatPlural')
       ->willReturnCallback(function ($count, $singular, $plural, array $args = [], array $options = []) {