Missing support for Chinese Traditional and Chinese simplified languages

[yarick2000]

FYI, I'm creating the following ticket basing on @Jotschi request in Gitter.
I wasn't able to setup Chinese Traditional and Chinese Simplified languages in current UI. Though I was following the guide I'm getting the following message in browser console:
Uncaught Error: [$injector:modulerr] Failed to instantiate module meshAdminUi due to:
Error: [$injector:modulerr] Failed to instantiate module meshAdminUi.common due to:
Error: [$injector:modulerr] Failed to instantiate module meshAdminUi.common.i18n due to:
Error: i18nServiceProvider#setAvailableLanguages: "zh-hans" is not a valid ISO-639-1 code.

Basing on google results zh-Hans and zh-Hant are correct codes for those two languages

[michaelbromley]

The problem is that the reference above is incorrect - the code zh-Hant is an IETF language code rather than an ISO 638-1 code. It is a bit confusing since the IETF standard incorporates the ISO 638-1 standard as the first part of its code.

You can see here the full list of ISO 639-1 codes supported by the beta ui app.

Unfortunately this means that no distinction can be made between tradition and simplified Chinese variants.

[yarick2000]

Is there is a chance to implement IETF or what will be the best workaround in this case? Also, is it possible to extend functionality for custom languages and use them without binding to ISO 639-1?