Multi-language applications

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.

In OWIN, a mechanism similar to ASP.NET Core request localization is not supported.

Instead, you can use the Localizable presenter which can define a route parameter to persist the language chosen by the user.