Sorry but the behaviors you want aren't supported out-of-the-box. Of course modifying the source code is always a possible solution. On the matter of localization feature for the Tag property, there are several approaches which I could think
of but admittedly, they involve a lot of work. (I'm merely presenting possible options, not necessarily suggesting all of them :))
1. Create a wrapper class for the ValidationResult so that the wrapper class has localization feature for the Tag property.
2. Create custom validators wrapping the existing validators
3. Create custom attributes which allows you to set the Tag property to the key in the resource file, pretty much similar to how you use the MessageTemplateResource and MessageTemplateResourceType properties.
Obviously, the easiest would be the first one but I'm not sure if it will violate your design or any of your specific requirement.
On your second concern, I assume you're using the ValidationCallhandler. The exception message generated by this handler is "Parameter validation failed." and unfortunately, this isn't configurable as well. You would have to create your custom
call handler to accomplish what you want.
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