Model binding and localization in ASP.NET MVC2

When creating an MVC site catering for different cultures, one option for persisting the culture value from one page to the next is by using an extra route value containing some form of identifier for the locale e.g.

/en-gb/Home/Index
/en-us/Cart/Checkout
/it-it/Product/Detail/1234

Here just using the Windows standard culture names based on RFC 4646 but you could use some other standard or your own custom codes. This method doesn’t rely on sessions or cookies and also has the advantage that the site can be spidered in each supported language.

Creating a base controller class for your site allows you to override one of its methods in order to set your current culture. For example if you amend your route configuration to "{locale}/{controller}/{action}/{id}" you could do the following:

string locale = RouteData.GetRequiredString("locale");
CultureInfo culture = CultureInfo.CreateSpecificCulture(locale);
Thread.CurrentThread.CurrentCulture = culture;
Thread.CurrentThread.CurrentUICulture = culture;

It's important to set both CurrentCulture and CurrentUICulture as ResourceManager, used for retrieving values form localized .resx files, will refer to CurrentUICulture whereas most other formatting routines use CurrentCulture.

Once our culture is set, when we output values in our views ResourceManager can pick up our culture specific text translations from the correct .resx file and dates and currency values will be correctly formatted. String.Format("{0:s}", DateTime.Now), with "s" being the format string for a short date, will produce mm/dd/yyyy for en-US versus dd/mm/yyyy for en-GB.

This isn't the end of the story however, the problem arises of where in the controller do you perform your culture setting. It can't happen in the constructor because the route data isn't yet available so instead we could put it in an override of OnActionExecuting. This will seem to work fine for values output in your views but you come across a gotcha within model binding. Create a textbox in a form which binds to a DateTime and you'll end up with the string value being parsed using the default culture of the server. Using the US and UK dates example where your server's default culture is US but your site is currently set to UK. If you try to enter a date of 22/01/2010 you'll get a model validation error because it's being parsed as the US mm/dd/yyyy and 22 isn't a valid value for the month. Model binding happens before OnActionExecuting so that's no good.

A bit of digging around in Reflector and the Initialize method comes out as probably the best candidate for this as it is where the controller first receives route data and it occurs before model binding. We end up with something like (exception handling omitted for brevity):

protected override void Initialize(RequestContext requestContext) 
{
    base.Initialize(requestContext);
    string locale = RouteData.GetRequiredString("locale");
    CultureInfo culture = CultureInfo.CreateSpecificCulture(locale);
    Thread.CurrentThread.CurrentCulture = culture;
    Thread.CurrentThread.CurrentUICulture = culture;
 }

Both model binding and output of values will now be using the correct culture.