Major Description
Because validation messages are defined in terms of a properties file, there isn't an avenue for introducing new, localized, messages (that can then be overridden).
Ideally, there should be a configuration point that allows new messages to be defined; the ValidationMessages interface should be aware of these messages and search them. Assuming the configuration was searched before ValidStrings.properties, this would also provide an easy way to override a default validation message throughout the application.