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Multi-language applications

DotVVM supports localization and comes with many features that help building multi-language applications.

Request culture

When DotVVM serializes the viewmodel, it includes an information about the current thread culture which was used to process the request. This information is then used on the client so the formatting and other features work the same as on the server.

If you use any control which works with numeric or date values (e.g. Literal with its FormatString property), or use the ToString method in a value binding, the page needs to know which culture should be used in order to apply the correct format.

Default application culture

In the configuration of DotVVM, you can specify the default culture which is used for all requests. The best way is to set this value in the DotvvmStartup.cs file using the following code:

config.DefaultCulture = "en-US";

Switching cultures

If your website supports multiple languages and cultures, you need to store the language the user has selected somewhere. It is common to detect the language from the Accept-Language header, and when the user chooses a different language, store the selection in cookies or include it in the URL.

In ASP.NET Core, the preferred way for handling this is using the Request localization middleware. You can configure the supported languages, the storage of the selected language, and so on.

First, configure the request localization in ConfigureServices in Startup.cs:

public void ConfigureServices(IServiceCollection services)
{
    ... 

    services.Configure<RequestLocalizationOptions>(options =>
    {
        var supportedCultures = new[]
        {
            new CultureInfo("en"),
            new CultureInfo("cs")
        };
        options.DefaultRequestCulture = new RequestCulture(culture: "en", uiCulture: "en");
        options.SupportedCultures = supportedCultures;
        options.SupportedUICultures = supportedCultures;
    });
}

Then, register the request localization middleware before the call to UseDotVVM:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    app.UseRequestLocalization();   // must be before UseDotVVM
    ...
    app.UseDotVVM<DotvvmStartup>(env.ContentRootPath);
}

Now, the request localization middleware will try to detect the language from the Accept-Language HTTP header, or from a cookie.

To switch the language, you need to store the language preference in the cookie:

public void SwitchLanguage(string language)
{
    Context.GetAspNetCoreContext().Response.Cookies
        .Append(
            CookieRequestCultureProvider.DefaultCookieName,
            CookieRequestCultureProvider.MakeCookieValue(new RequestCulture(language))
        );
    Context.RedirectToLocalUrl(Context.HttpContext.Request.Url.PathAndQuery);
}

See the DotVVM request localization sample for more info.

See also