Enable syncing of zh-tw and zh-hk for MediaWiki

Replying here on David's behalf because he can't get LQT to work for him:

There are real language differences between zh-TW and zh-HK in the MediaWiki files. For example, the word for 'bot' is '機器人' in Taiwan but '機械人' in Hong Kong. Note that both are written in Traditional Chinese (the Simplified Chinese equivalents would be 机器人 and 机械人).

Therefore using only one set of translations for Traditional Chinese would mean showing some wrong words in the Hong Kong interface (or the Taiwan one). I believe the same issue applies for Simplified Chinese: some the words used in zh-CN and zh-SG are different.

The variants could be labelled 'zh-Hant' and 'zh-Hant-HK' respectively, which would be BCP47-compliant. (Similarly, 'zh-Hans' and 'zh-Hans-SG' would be appropriate).