XmlLanguage.GetEquivalentCulture doesn't match System.Globalization.CultureInfo

• .NET Core Version: 5.0
• Windows version: windows 10
• Does the bug reproduce also in WPF for .NET Framework 4.8?: No
• Is this bug related specifically to tooling in Visual Studio (e.g. XAML Designer, Code editing, etc…)? No

Problem description: XmlLanguage.GetEquivalentCulture() no longer matches new System.Globalization.CultureInfo. When compiling with netcoreapp3.1 string1 and string2 in the code block below are the same. With net5.0 they are different.

var string1 = (-10).ToString("C2", new System.Globalization.CultureInfo("en-US"));
var string2 = (-10).ToString("C2", System.Windows.Markup.XmlLanguage.GetLanguage("en-US").GetEquivalentCulture());

Actual behavior: string1 and string2 difer

Expected behavior: string1 and string2 are the same

Minimal repro: See description

[miloush]

Here we go: https://learn.microsoft.com/en-us/dotnet/core/extensions/globalization-icu

<ItemGroup>
	<RuntimeHostConfigurationOption Include="System.Globalization.UseNls" Value="true" />
</ItemGroup>

should restore the .NET Framework behavior.

[innominate227]

Here is a reop showing the issue: https://github.com/innominate227/WpfCurrencyNegativePatternIssue. And screenshot of what I see when debugging.