The following:

_ = new CultureInfo(CultureInfo.InvariantCulture.TwoLetterISOLanguageName)

Will throw the error CultureNotFoundException: Culture name iv is not supported. (This happens with the ThreeLetterISOLanguageName "IVL" as well).

This seems... odd, given that _ = new CultureInfo(string.Empty) returns the CultureInfo.InvariantCulture object just fine.

This edge case is not indicated in the documentation.

Why is this important?

Suppose I create a list of CultureInfo that is supported by my application and include the InvariantCulture as a fallback (which would happen if the culture name supplied is an empty string, either accidentally or intentionally). If I serialize this list as cultureList.Select(c => c.TwoLetterISOLanguageName) and then attempt to load it via langNames.Select(n => new CultureInfo(n)), the invariant culture which will have serialized as iv then cannot be deserialized without edge-case detection to convert iv back to an empty string and will instead throw an error I could not have anticipated.