When a user fails to sign on, PingFederate parses the response from the data store and shows a corresponding error message on the login page. In the password credential validator configuration, you can customize which error message is triggered based on the response from the data store.
By adding rules that check the data store response for specific text, you can trigger one of the default error messages or a custom error message that you define.
The default error messages are defined in <pf_install>/pingfederate/server/default/conf/language-packs/pingfederate-messages.properties. This file is part of the PingFederate localization framework and can be adapted to other languages. See Localizing messages for end users in the PingFederate documentation.