To offer a website in multiple languages using ASP.NET MVC 4 , we simply need to add some resource.resx files to our project. Based on the language of the browser, IIS will match the localization resource. However, what if we want to give the choice to the user?

The goal

One pattern often used to achieve this, is to split the resource based on the URL. Example:
http://www.DomainName.com/EN/About for the English path
http://www.DomainName.com/FR/About for the French path

The needs

We will need something to grab the desired language from the URL and set it as the current language.

The Solution

First, let's add a new route. Asp.Net uses routing to parse the URL and to extract information from it, while keeping the displayed URL more user friendly. The default route is {controller}/{action}/{id}.

So without a new route, our language will be treated as a Controller name; but that’s no good.
The route we want is {lang}/{controller}/{action}/{id}. We could just replace the default, but then what would happen to "normal" calls?

The best thing to do is to add our localized route first and keep the default second. The way the routing works, it will use the first route that matches. Since we will use the two-letter code for chosen language, lets add the first part {lang}, which must be two characters long to be considered valid. You can see this in the code where I define a constraint using the following Regex: "^[a-zA-Z]{2}$".

Now that we have the language, we must change the user interface culture of the current thread. I decided to use an Attribute, making it easy to use. Under the Filter folder add a new class which inherits from ActionFilterAttribute. This method will check if "lang" is available from RouteData. If lang is present it will change the currentUICulture of the current thread. If "lang" is not part of the URL, then it will set it to the default.

We could put the [Localization] attribute on all controller classes, but a best practice is to create a BaseController class and use it there.

You can now change the language of the entire website by changing the URL.

Use it everywhere

To use it in the view and the controller it's easy; just add the namespace and just type Resources.NameOfYourResourceString.
To use it in the validation and the generated code from the model, we could use something like this:

This way, in the view, the code will still stay clean and simple.

@Html.LabelFor(model.UserName)

This Article shows how to use the Latest ASP.net MVC 5 Attribute Routing's Route Constraints with your Application. You can read the first part of this Article here 'Attribute Routing With ASP.net MVC 5. If you want to be more familiar with ASP.NET MVC 5, you should try HostForLife.eu.

How to set Route Constraints ?
It allows you to restrict the parameters in the route template are matched
The syntax is {parameter:constraint}

PetController.cs

public class PetController : Controller
{
[Route("Pet/{petId:int}")]
public ActionResult GetSpecificPetById(int petId)
{
return View();
}
}

Key points of the above code:
- In the above example, /Pet/8 will Route to the “GetSpecificPetById” Action.
- Here the route will only be selected, if the "petId" portion of the URI is an integer.
Above Route on Browser is as below

The following diagram shows the constraints that are supported

How to apply multiple constraints to a parameter ?

You can apply multiple constraints to a parameter, separated by a colon.
Well,It's like this  [Route("Pet/{petId:int:min(1)}")]

PetController.cs
public class PetController : Controller
{
[Route("Pet/{petId:int:min(1)}")]
public ActionResult GetSpecificPetById(int petId)
{
return View();
}
}

Key points of the above code
In the above example,You can't use  /Pet/10000000000 ,because it is larger than int.MaxValue
And also you can't use /Pet/0 ,because of the min(1) constraint.

How to Specifying that a parameter is Optional ?
You can do it by Specifying that a parameter is Optional (via the '?' modifier).
This should be done after inline constraints.
Well,it's like this  [Route("Pet/{message:maxlength(4)?}")]

PetController.cs

// eg: /Pet/good
[Route("Pet/{message:maxlength(4)?}")]
public ActionResult PetMessage(string message)
{
return View();
}

Key points of the above code
In the above example, /Pet/good and /Pet will Route to the “PetMessage” Action.
The route /Pet also works hence of the Optional modifier.
But /Pet/good-bye will not route above Action , because of the maxlength(4) constraint.

Above Routes on Browser are as below