Report [[User:Cwlin0416]]'s vandalism

For this one, the Gan Chinese and the Classical Chinese are fallback to the Traditional Chinese. So in general those two are not intended to use as the Taiwan Chinese vocabulary, where they were translated in Traditional Chinese translation, are not suitable to localise them there.

So the same reason that "Why don't fallback yue to zh-hant or zh-hk"?

The reason for Yue is similar for that so I oppose the Yue language to fallback to zh-Hant.

By the way MediaWiki never disabled the zh-CN/zh-TW interface so those languages can be translated if the translations are different to their parent language.

Never disabled? Although, per phab:T51898 there's a bypass way.

PS: If zh-hant is not an opinion then how about zh-hk?

On the other hand: "Classical Chinese fallback to the Traditional Chinese" not currently, see phab:T125373.

For example, the phrase "User" can both implemented in Chinese in General, so in both zh-Hant and zh-Hans should be use 『用戶』 and 『用户』 respectively. However in Taiwan terms, 『使用者』 are used more common so the term 『使用者』 should be translated in zh-TW instead of zh-Hant.

That's the similar terms "robot" or "bot" which differs between the Chinese Terms. In general, 『機器人』 or 『机器人』 are used in zh-Hant and zh-Hans respectively. In Hong Kong, the term 『機械人』 is used instead so this one should be translated in zh-HK but not for zh-Hant.