Moving from https://github.com/dotnet/cli/issues/4050 on behalf of @ryanbrandenburg.

Steps to reproduce

1. Register a custom culture using something like sysglobl.dll and:

var car1 = new CultureAndRegionInfoBuilder("ru-US", CultureAndRegionModifiers.None);
car1.LoadDataFromCultureInfo(CultureInfo.CreateSpecificCulture("ru-RU"));
car1.LoadDataFromRegionInfo(new RegionInfo("en-US"));

car1.CultureEnglishName = "Russion (United States)";
car1.CultureNativeName = "русский (США)";
car1.CurrencyNativeName = "Доллар (США)";
car1.RegionNativeName = "США";

// Register the culture.
try
{
    car1.Register();
}
catch (InvalidOperationException)
{
    // Swallow the exception: the culture already is registered.
}

1. Create a new ASP.NET Core Web Application (.NET Core)
2. Create two resources, one named Resource.en-US.resx and one named Resource.ru-US.resx
3. Build the project.
4. Open bin/Debug/net451
5. Observe that a en-US folder is present and has a dll and that ru-US is missing

Expected behavior

Any culture which will work with new CultureInfo("culture-NAME") (which custom cultures do once registered as above) should create a folder and dll which can be used in localization.

Actual behavior

Satellite assemblies are only created for original cultures, not for custom cultures.

Environment data

dotnet --info output:
.NET Command Line Tools (1.0.0-preview2-003121)

Product Information:
Version: 1.0.0-preview2-003121
Commit SHA-1 hash: 1e9d529

Runtime Environment:
OS Name: Windows
OS Version: 10.0.10586
OS Platform: Windows
RID: win10-x64