Update to Drupal 8.2.4. For more information, see https://www.drupal.org/project/drupal/releases/8.2.4

core/lib/Drupal/Core/StringTranslation/Translator/CustomStrings.php

@@ -3,6 +3,7 @@
 namespace Drupal\Core\StringTranslation\Translator;
 
 use Drupal\Core\Site\Settings;
+use Drupal\Core\DependencyInjection\DependencySerializationTrait;
 
 /**
  * String translator using overrides from variables.
@@ -12,6 +13,8 @@ use Drupal\Core\Site\Settings;
  */
 class CustomStrings extends StaticTranslation {
 
+  use DependencySerializationTrait;
+
   /**
    * The settings read only object.
    *