Issue #3278852: Use $this->t()

src/Form/FillPdfFormForm.php

@@ -414,7 +414,7 @@ class FillPdfFormForm extends ContentEntityForm {
           'warning' => [$fillpdf_form_fields_empty_message],
         ],
         '#status_headings' => [
-          'warning' => t('Warning message'),
+          'warning' => $this->t('Warning message'),
         ],
       ];
     }