diff -u b/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php b/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php
--- b/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php
+++ b/core/lib/Drupal/Core/StringTranslation/TranslationWrapper.php
@@ -61,7 +61,7 @@
   public function __construct($string, array $arguments = array(), array $options = array()) {
     // We disallow passing in non-string values such as when we translate
     // an already translated value.
-    assert('!is_string($string)', 'Non-string value passed in.');
+    assert('is_string($string)', 'Non-string value passed in: ' . (string) $string);
     $this->string = $string;
     $this->arguments = $arguments;
     $this->options = $options;
only in patch2:
unchanged:
--- a/core/modules/config_translation/config_translation.module
+++ b/core/modules/config_translation/config_translation.module
@@ -115,7 +115,7 @@ function config_translation_config_translation_info(&$info) {
         $info[$entity_type_id . '_fields'] = array(
           'base_route_name' => "entity.field_config.{$entity_type_id}_field_edit_form",
           'entity_type' => 'field_config',
-          'title' => '!label field',
+          'title' => '@label field',
           'class' => '\Drupal\config_translation\ConfigFieldMapper',
           'base_entity_type' => $entity_type_id,
           'weight' => 10,
@@ -144,7 +144,7 @@ function config_translation_config_translation_info(&$info) {
     $info[$entity_type_id] = array(
       'class' => '\Drupal\config_translation\ConfigEntityMapper',
       'base_route_name' => $base_route_name,
-      'title' => '!label !entity_type',
+      'title' => '@label @entity_type',
       'names' => array(),
       'entity_type' => $entity_type_id,
       'weight' => 10,
only in patch2:
unchanged:
--- a/core/modules/config_translation/src/ConfigEntityMapper.php
+++ b/core/modules/config_translation/src/ConfigEntityMapper.php
@@ -158,7 +158,7 @@ public function getTitle() {
     // current page language. The title placeholder is later escaped for
     // display.
     $entity_type_info = $this->entityManager->getDefinition($this->entityType);
-    return $this->t($this->pluginDefinition['title'], array('!label' => $this->entity->label(), '!entity_type' => $entity_type_info->getLowercaseLabel()));
+    return $this->t($this->pluginDefinition['title'], array('@label' => $this->entity->label(), '@entity_type' => $entity_type_info->getLowercaseLabel()));
   }
 
   /**