RequestCultureProvider sets an unsupported culture when the request is not supported and the default is not defined or not supported.

[Bartmax]

Helping someone with an issue on Jabbr about localization, I found this strange (at least for me) behavior.

RequestLocalizationOptions localizationOptions = new RequestLocalizationOptions()
{
  SupportedCultures = new List<CultureInfo>
  {
    new CultureInfo("nl-NL")
  },
  SupportedUICultures = new List<CultureInfo>
  {
    new CultureInfo("nl-NL")
  }
  //, DefaultRequestCulture = new RequestCulture(new CultureInfo("nl-NL"), new CultureInfo("nl-NL"))
};
app.UseRequestLocalization(localizationOptions);

------------------------
services.AddLocalization();
services.AddMvc().AddViewLocalization();

note the commented line

With this cshtml (in layout or index):

<h1>UICulture: @System.Globalization.CultureInfo.CurrentUICulture.Name</h1> // outputs: en-US 
<h1>Culture: @System.Globalization.CultureInfo.CurrentCulture.Name</h1> // outputs: es-UY

According to the documentation here: https://github.com/aspnet/Localization/blob/dev/src/Microsoft.AspNet.Localization/RequestLocalizationOptions.cs#L38-L54

This is not expected behavior. Those cultures are not supposed to be supported by the application.

Uncommenting the commented line (DefaultRequestCulture) I get the expected output:

DefaultRequestCulture = new RequestCulture(new CultureInfo("nl-NL"), new CultureInfo("nl-NL"))
UICulture: nl-NL
Culture: nl-NL

Looking at source code, I found that a 'premature' fallback to default culture.
https://github.com/aspnet/Localization/blob/dev/src/Microsoft.AspNet.Localization/RequestCultureProvider.cs#L42-L50 without checking if the Default is supported.

I think the workflow should be more like (not real code)

var culture = Options.SupportedCultures == null || !Options.SupportedCultures.Any() || Options.SupportedCultures.Contains(result.Culture)
    ? result.Culture
    : Options.SupportedCultures.Contains(Options.DefaultRequestCulture.Culture)
    ? Options.DefaultRequestCulture.Culture
    : Options.SupportedCultures.First();

var uiCulture =  Options.SupportedUICultures == null || !Options.SupportedUICultures.Any() || Options.SupportedUICultures.Contains(result.UICulture)
    ? result.UICulture
    : Options.SupportedUICultures.Contains(Options.DefaultRequestCulture.UICulture)
    ? Options.DefaultRequestCulture.UICulture
    : Options.SupportedUICultures.First();

 result = new RequestCulture(culture, uiCulture);

I'm assuming Empty List = null here.

[Bartmax]

This is related: #38

[hishamco]

It's a bug :(

[hishamco]

@Bartmax can you try this

if (requestCulture == null || Options == null)
{
    return null;
}

var result = requestCulture;

if (Options.SupportedCultures?.Contains(result.Culture) == false)
{
    if (Options.SupportedCultures.Contains(Options.DefaultRequestCulture.Culture))
    {
         return new RequestCulture(Options.DefaultRequestCulture.Culture);
    }
    else
    {
        return new RequestCulture(Options.SupportedCultures?.Count > 0 ?
            Options.SupportedCultures[0] : Options.DefaultRequestCulture.Culture);
    }
}

if (Options.SupportedUICultures?.Contains(result.UICulture) == false)
{
    if (Options.SupportedUICultures.Contains(Options.DefaultRequestCulture.UICulture))
    {
         return new RequestCulture(Options.DefaultRequestCulture.UICulture);
    }
    else
    {
         return new RequestCulture(Options.SupportedUICultures?.Count > 0 ?
             Options.SupportedUICultures[0] : Options.DefaultRequestCulture.UICulture);
    }
}
return result;

[Bartmax]

Looks good, not sure what will works as expected if we have:

  SupportedCultures = new List<CultureInfo>
  {
    new CultureInfo("es-UY")
  },
  SupportedUICultures = new List<CultureInfo>
  {
    new CultureInfo("nl-NL")
  }

I don't think it will be a common scenario but...

because we return earlier on Culture without even checking at UICulture. I guess best way to tell is to have some unit test.

[hishamco]

You are right @Bartmax, let me revise the code snippet and come back to you

[hishamco]

@kirthik can you look into this if you don't mind, seems it's a critical issue