Updated Wiki: Getting started

public sealed class DataAnnotationsLocalizer
{
    public static void SetDefaultResourceType(Assembly assembly, Type resources, params Type[] localizableAttributeTypes)
    {
        foreach (var item in GetTypesInNamespace(assembly, null))
        {
            SetDefaultResourceType(item, resources, localizableAttributeTypes);

        }
    }

    public static void SetDefaultResourceType(Assembly assembly, string nameSpace, Type resources, params Type[] localizableAttributeTypes)
    {
        foreach (var item in GetTypesInNamespace(assembly, nameSpace))
        {
            SetDefaultResourceType(item, resources, localizableAttributeTypes);
        }
    }

    public static void SetDefaultResourceType(Type item, Type resources, params Type[] localizableAttributeTypes)
    {
        foreach (PropertyDescriptor prop in TypeDescriptor.GetProperties(item))
        {
            foreach (var localizableAttrType in localizableAttributeTypes)
            {
                Attribute dAttr = ((Attribute)prop.Attributes[localizableAttrType]);
                if (dAttr != null)
                {
                    if (dAttr is DisplayAttribute && (dAttr as DisplayAttribute).Name != null)
                        ((DisplayAttribute)dAttr).ResourceType = resources;
                    if (dAttr is ValidationAttribute && (dAttr as ValidationAttribute).ErrorMessageResourceName != null)
                        ((ValidationAttribute)dAttr).ErrorMessageResourceType = resources;

                }
            }

        }
    }

public class DemoController : Controller
{
    //
    // GET: /Demo/

    public ActionResult Index()
    {
        return View(new Person());
    }

    [HttpPost]
    public ActionResult Save(Person p)
    {
        return View("Index", p);
    }

    public ActionResult SetLanguage(string language)
    {
        Session["SelectedCultureId"] = language;
        return RedirectToAction("Index");
    }

   

    protected override void Initialize(System.Web.Routing.RequestContext requestContext)
    {
        string culture = (string)requestContext.HttpContext.Session["SelectedCultureId"];
        if (culture != null)
        {
            System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo(culture);
            System.Threading.Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo(culture);
        }
        base.Initialize(requestContext);
    }

}

@model MvcDemoApp.Models.Person
@{
    ViewBag.Title = "Demo";
    Layout = "~/Views/Shared/_Layout.cshtml";
}

<h2>Localization via T4 Template Demo</h2>

@Html.ActionLink("Englisch", "SetLanguage", "Demo", new { language = "en-us" }, null)
@Html.ActionLink("Deutsch", "SetLanguage", "Demo", new { language = "de-de" }, null)

@using(Html.BeginForm("Save", "Demo"))
{
    @Html.ValidationSummary(true);
<fieldset>
    <legend>Person</legend>
    @Html.LabelFor(m => Model.FirstName)
    @Html.EditorFor(m => Model.FirstName)
    @Html.ValidationMessageFor(m => Model.FirstName)
    <br />
    @Html.LabelFor(m => Model.LastName)
    @Html.EditorFor(m => Model.LastName)
    @Html.ValidationMessageFor(m => Model.LastName)
    <br />
    @Html.LabelFor(m => Model.Phone)
    @Html.EditorFor(m => Model.Phone)
    @Html.ValidationMessageFor(m => Model.Phone)
    <br />
    @Html.LabelFor(m => Model.Address)
    @Html.EditorFor(m => Model.Address)
    @Html.ValidationMessageFor(m => Model.Address)
    <br />
    <input type="submit" name="btnSubmit" id="SubmitButton" value="Submit" />
</fieldset>
}

public class Person:IValidatableObject  
{
    [Display(Name = DisplayNames.Keys.FirstName)]
    [Required(ErrorMessageResourceName=ErrorMessages.Keys.CustomModelError)]
    public string FirstName { get; set; }

DataAnnotationsLocalizer.SetDefaultResourceType(typeof(Person).Assembly, typeof(ErrorMessages),
    typeof(RequiredAttribute));

class Program
{
    static void Main(string[] args)
    {
        DataAnnotationsLocalizer.SetDefaultResourceType(typeof(Person).Assembly, typeof(DisplayNames), typeof(DisplayAttribute));
        DataAnnotationsLocalizer.SetDefaultResourceType(typeof(Person).Assembly, 
            typeof(ErrorMessages),
            typeof(RequiredAttribute), 
            typeof(MaxLengthAttribute));

        DataAnnotationsLocalizer.ReplaceDefaultLocalizedMessage<RequiredAttribute>(
            typeof(Person).Assembly, typeof(Person).Namespace, typeof(ErrorMessages), ErrorMessages.Keys.RequiredMessage);
        DataAnnotationsLocalizer.ReplaceDefaultLocalizedMessage<MaxLengthAttribute>(
            typeof(Person).Assembly, typeof(Person).Namespace, typeof(ErrorMessages), ErrorMessages.Keys.MaxLengthMessage);


        try
        {
            System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("de-de");
            System.Threading.Thread.CurrentThread.CurrentCulture = new System.Globalization.CultureInfo("de-de");

            Person p = new Person { Address = "asdkjalsdkjalskdjasldkjalskdjaskldjaskldjalasdasdasdasdasdasdskdjalskdjaskldjalsdkjalsdk" };

            List<ValidationResult> res = new List<ValidationResult>();
            Validator.TryValidateObject(p, new ValidationContext(p, null, null), res, true);

            foreach (var item in res)
            {
                Console.WriteLine(item.ErrorMessage);
            }
        }
        catch (ValidationException)
        {

        }

        Console.ReadLine();

    }
}