these two variants doesn't have full conversion

Can you clarify what you mean by this? What specifically is not converted?
The different Chinese variants are absolutely intended for end users, so if something is not converted properly, we would like to know.

https://meta.wikimedia.org/wiki/Wikipedias_in_multiple_writing_systems#Chinese
"has different localized vocabularies and syntaxes"
zh-hans and zh-hant provide syntaxes conversion but not vocabularies conversion.
zh-cn and 5 other variants provide both vocabularies conversion and syntaxes conversion.
If users use zh-hans or zh-hant variants, they may be confused when they see unlocalized vocabularies.

In T305319#7828348, @Dbrant wrote:

these two variants doesn't have full conversion

Can you clarify what you mean by this? What specifically is not converted?
The different Chinese variants are absolutely intended for end users, so if something is not converted properly, we would like to know.

What @Xiplus says is right. Chinese Wikipedia's conversion system consists of two parts, simp-trad (syntax) conversion and regional word (vocabulary) conversion.

For instance, the movie The Shawshank Redemption is translated to “肖申克的救赎” in Chinese (Simplified, China) [zh-cn], but “刺激1995” in Chinese (Traditional, Taiwan) [zh-tw] and “月黑高飛” in Chinese (Traditional, Hong Kong) [zh-hk].

What should it be displayed as if a user choose zh-hant without specifying their region? As a result, the regional word conversion will just not work, resulting in unlocalized terms and vocabularies.

EDIT: Also, in Special:Perference in Chinese Wikipedia, we have a warning below the variant selection dropdown:

For a better reading experience, if not for testing purpose, we suggest to choose other region-specific Chinese variants rather than zh, zh-hant, zh-hans.

This can also reflect the fact that those three variants are for technical purpose only.

The screenshots below provides more details about this. I hope it would help.

zh-cn	zh-tw	zh-hk	zh-hant
“肖申克的救赎”	“刺激1995”	“月黑高飛”	“肖申克的救贖”
✔️	✔️	✔️	❌ unlocalized term, literal conversion from “肖申克的救赎”, will lead to confusion

Moreover, after removing them, we should decide what to do with existing options where users have chosen zh-hans and zh-hant as their preferred languages.

Before we have provided the full Chinese language variants options in the app for over one year, the zh-hant and zh-hans were the original ones that were the available Chinese language variants options in the app.

Not sure what would be the default region-wise language variants for Traditional Chinese and Simplified Chinese, and I think it is not appropriate to change them automatically without notifying the users.

I suggest keeping the current setting which shows the entire list of language variants but also introducing a toolbar or some other messages interfaces that can inform the user about language variants options.

cc @JTannerWMF

In T305319#7832921, @cooltey wrote:

Moreover, after removing them, we should decide what to do with existing options where users have chosen zh-hans and zh-hant as their preferred languages.

Before we have provided the full Chinese language variants options in the app for over one year, the zh-hant and zh-hans were the original ones that were the available Chinese language variants options in the app.

Not sure what would be the default region-wise language variants for Traditional Chinese and Simplified Chinese, and I think it is not appropriate to change them automatically without notifying the users.

I suggest keeping the current setting which shows the entire list of language variants but also introducing a toolbar or some other messages interfaces that can inform the user about language variants options.

cc @JTannerWMF

I think we can prompt users about the change and ask them to select from one of the precise variants if they chose zh-hans and zh-hant.

As I have mentioned above, displaying zh-hant and zh-hans to users is not appropriate because they have incomplete conversion and is intended for technical purposes only. Now we already have full variant support for Chinese language, I believe it is time to phase out those two variants now.

@WhitePhosphorus Do you have any interest in implementing this? Thanks.

I'm moving this back to Triage. Tracking indicates that the fix is on the backend, but it looks to me like this requires client-side changes.