diff -u b/core/modules/outside_in/src/Form/SystemBrandingOffCanvasForm.php b/core/modules/outside_in/src/Form/SystemBrandingOffCanvasForm.php
--- b/core/modules/outside_in/src/Form/SystemBrandingOffCanvasForm.php
+++ b/core/modules/outside_in/src/Form/SystemBrandingOffCanvasForm.php
@@ -43,7 +43,7 @@
    */
   public function __construct(ConfigFactoryInterface $config_factory, TranslationInterface $string_translation) {
     $this->configFactory = $config_factory;
-    setStringTranslation($string_translation);
+    $this->setStringTranslation($string_translation);
   }
 
   /**