For reference "Each encompassed language's subtag SHOULD be used as the primary      language subtag.  For example, a document in Mandarin Chinese      would be tagged "cmn" (the subtag for Mandarin Chinese) in      preference to "zh" (Chinese)." https://www.ietf.org/rfc/bcp/bcp47.html#section-4.1.2
I don't oppose using `zh` for PRC and Taiwan. But this would be different in HK and Macau. 