TYPO3 Core

The method ranslateErrorMessage() in TYPO3\CMS\Extbase\Validation\Validator\AbstractValidator has parameter 1 to be the translation key and parameter 2 to be the extension name. So when you translated your error message with key and extension name in the past, you get your intended translation. In TYPO3 v13, there is at the very beginning a if condition, which says

if (!str_starts_with($translateKey, 'LLL:')) {
   return $translateKey;
}