CultureInfo.Name should explain three-letter language names

[svick]

The documentation for CultureInfo.Name says:

The culture name in the format languagecode2-country/regioncode2 [..]. languagecode2 is a lowercase two-letter code derived from ISO 639-1.

This is not correct. For many languages, the language code part is three letters. (Also, what does "derived" actually mean?)

The documentation for CultureInfo.TwoLetterISOLanguageName keeps talking about "two-letter code", but it also clarifies this a bit:

If ISO 639-1 does not define a two-letter language code for a particular culture, the TwoLetterISOLanguageName property returns a string that consists of three or more letters.

As far as I can tell, for all languages with three-letter codes, their ISO 639-3 code is used.

I think this should be clarified:

1. Both Name and TwoLetterISOLanguageName should make it clear that the name can be two or three letters.
2. The documentation should specify that ISO 639-3 codes are used for three-letter languages.

Tagging subscribers to this area: @tarekgh, @safern
See info in area-owners.md if you want to be subscribed.

Issue Details

---

The documentation for CultureInfo.Name says:

The culture name in the format languagecode2-country/regioncode2 [..]. languagecode2 is a lowercase two-letter code derived from ISO 639-1.

This is not correct. For many languages, the language code part is three letters. (Also, what does "derived" actually mean?)

The documentation for CultureInfo.TwoLetterISOLanguageName keeps talking about "two-letter code", but it also clarifies this a bit:

If ISO 639-1 does not define a two-letter language code for a particular culture, the TwoLetterISOLanguageName property returns a string that consists of three or more letters.

As far as I can tell, for all languages with three-letter codes, their ISO 639-3 code is used.

I think this should be clarified:

1. Both Name and TwoLetterISOLanguageName should make it clear that the name can be two or three letters.
2. The documentation should specify that ISO 639-3 codes are used for three-letter languages.

Author:	svick
Assignees:	-
Labels:	Pri3, area-System.Globalization, :watch: Not Triaged
Milestone:	-

[tarekgh]

@svick are you interested to submit a PR?

[wenz]

Took a shot at this