Cannot get basic localization to work with ASP.NET 5 - localization

Question

I'm trying localize my ASP.NET 5 / MVC 6 (RC1) project. Unfortunately the official documentation is still missing so I based my experiments mainly on this and this blog posts.
Here is what I did: In Configure (Startup.cs) I have
app.UseRequestLocalization(new RequestLocalizationOptions
{
RequestCultureProviders = new List<IRequestCultureProvider>
{
new CustomRequestCultureProvider(httpContext => Task.FromResult(new ProviderCultureResult("de-CH"))),
new AcceptLanguageHeaderRequestCultureProvider()
}
}, new RequestCulture("en-US"));
Note that the first entry in my RequestCultureProviders list always returns the de-CH culture. So I would expect that the AcceptLanguageHeaderRequestCultureProvider as well as the default RequestCulture (en-US) have no influence.
However when I look at
HttpContext.Features.Get<IRequestCultureFeature>().RequestCulture.Culture.Name;
in some controller action, its value is en-US and not the expected de-CH.
I then tried to change the default RequestCulture in Configure from en-US to de-DE and now when I look at
HttpContext.Features.Get<IRequestCultureFeature>().RequestCulture.Culture.Name;
in my controller action, it has the value de-DE.
So the question is: Why does ASP.NET fall back to the default culture instead of using the culture de-CH provided by my CustomRequestCultureProvider?

Answer 1

It seems you must also include "de-CH" in the list of supported cultures. For example, the following returns "de-CH" as the culture, but if I comment out the lines setting SupportedCultures, it displays "en-US". In an MVC application, you might also have to set SupportedUICultures.
public void Configure(IApplicationBuilder app)
{
app.UseIISPlatformHandler();
var requestLocalizationOptions = new RequestLocalizationOptions
{
SupportedCultures = new List<CultureInfo>
{
new CultureInfo("en-US"),
new CultureInfo("de-CH")
},
RequestCultureProviders = new List<IRequestCultureProvider>
{
new CustomRequestCultureProvider(httpContext => Task.FromResult(new ProviderCultureResult("de-CH"))),
new AcceptLanguageHeaderRequestCultureProvider()
}
};
app.UseRequestLocalization(requestLocalizationOptions, new RequestCulture("en-US"));
app.Run(async (context) =>
{
var envName = context.Features.Get<IRequestCultureFeature>().RequestCulture.Culture.Name;
await context.Response.WriteAsync("Hello World! " + envName);
});
}
The description for the SupportedCultures property says a value of null indicates all cultures are supported and that null is the default, but testing indicates otherwise, as does the source:
/// <summary>
/// The cultures supported by the application. The <see cref="RequestLocalizationMiddleware"/> will only set
/// the current request culture to an entry in this list.
/// Defaults to <see cref="CultureInfo.CurrentCulture"/>.
/// </summary>
public IList<CultureInfo> SupportedCultures { get; set; } = new List<CultureInfo> { CultureInfo.CurrentCulture };