Language code changes over time: zh_CN -> zh_Hans

[Jean-Baptiste Holcroft <jean-baptiste at holcroft dot fr>]

Hi,

the Fedora community is migrating to the Weblate translation platform.
This translation platform uses zh_Hans, zh_Hant, zh_Hant_HK by default, 
instead of zh_CN, zh_TW and zh_HK.

If I understand correctly, we need to make sure the language code exists 
in glibc before deciding using the new code for Linux applications.

The issue is as follow: a translation platform can be used by many 
projects, not all using glibc, like Websites or mobile application who 
already are using the new code.

The web tells that the codes zh_CN, zh_TW, zh_HK are old codes and 
should be replaced by the new ones.
Multiple sources tends to confirm this (and show that other actors 
already did the move), the most relevant ones are:
https://www.w3.org/TR/i18n-html-tech-lang/#h2_langvalues
http://www.rfc-editor.org/rfc/bcp/bcp47.txt

And the replacement rule is also in the CLDR:
https://github.com/unicode-org/cldr/blob/ed7854cb6209678739712854a2df1cac732be540/common/supplemental/supplementalMetadata.xml#L177


What is the support status of these new language codes in Glibc?
If not supported, can we imagine to have backward compatibility while 
upstream projects migrate to the new language code?
I assume these are not the only language code renaming, what policy do 
you suggest concerning these?


Please do not hesitate to tell where this discussion should happen as 
this is my first contact with your community.


Thanks a lot for your help,
Jean-Baptiste