protected override void OnActionExecuting(ActionExecutingContext filterContext)
{
    var valueProviderResult = filterContext.Controller.ValueProvider.GetValue("<source parameter name>");

    //translation here, you can morph the value as you wish
    if (valueProviderResult != null)
    {
        filterContext.ActionParameters["<destination parameter name"] = yourTranslationService(valueProviderResult.AttemptedValue);
    }

    base.OnActionExecuting(filterContext);
}