C# - Xval Get Error Message From Resource File?

I'm working on a CMS system which uses a resource file to get information and errormessages from. The client side validation is working without problems, only it's not getting the errormessage from the resource file. While debugging i figured out xval seems to get the errormessages from a javascript file where the messages are set hard-coded. Is there some way to override this?

Below the code which should make the relation to the resourcefile en specify the error when the field is left empty.

[Property]
[Required(ErrorMessageResourceType = typeof(CMSMessages), ErrorMessageResourceName = "EnterValidMoney")]
public virtual Double ShippingCost { get; set; }