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

If there are previous translations in MediaWiki, they should probably be removed. I don't think we should enabled zh-cn and zh-tw. We've been using it like this for more than 8 years. I'll point Liangent here, a long time and knowledgable contributor to Chinese i18n.

Siebrand‎10:05, 10 April 2014
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