CultureInfo.GetCultureInfo("root") is an accepted but incomplete culture which can raise NullReferenceException on internals

[rjgotten]

Description

"und" is the correct BCP-47 tag for the "undetermined language" and maps correctly to CultureInfo.InvariantCulture when using CultureInfo.GetCultureInfo("und").

"root" is the alternative moniker used by CLDR.
When using CultureInfo.GetCultureInfo("root") it does not throw a CultureNotFoundException.
Rather it returns an incomplete unknown culture with LCID 4096.
And if one attempts to read NumberFormat off of it:

> System.Globalization.CultureInfo.GetCultureInfo("root").NumberFormat
System.NullReferenceException: Object reference not set to an instance of an object.
  + System.Globalization.NumberFormatInfo.InitializeInvariantAndNegativeSignFlags()
  + System.Globalization.CultureInfo.get_NumberFormat()

Reproduction Steps

Open any C# repl and execute:
System.Globalization.CultureInfo.GetCultureInfo("root").NumberFormat

Expected behavior

Either CultureInfo.GetCultureInfo("root") throws a CultureNotFoundException or it produces an actual intact culture.

Actual behavior

CultureInfo.GetCultureInfo("root") is accepted as a valid, recognized culture and does not throw a CultureNotFoundException - however what it produces is in fact not an actual intact culture.

Regression?

No response

Known Workarounds

No response

Configuration

.NET version: .NET 10
OS: Windows 11

Other information

No response

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[tarekgh]

@rjgotten, thanks for reporting it. If you are blocked by any mean, you may consider using und or Invariant culture for that. We can look at the NumberFormat issue when having root name. Or we can just map `root to Invariant culture.