In ServiceNow Portal (Service Portal / Employee Center), if you want to show language-based error messages without much custom development and as close as possible to OOTB (Out of the Box), use Message Translation and gs.getMessage(). Use System Localization Messages (Recommended): Navigate to: System Localization → Messages Create a message: Key: invalid_user_error Message (English): Invalid user selected. Create translations for the same key: Language: French → Utilisateur non valide sélectionné.