Getting back on topic, I was of the understanding (perhaps mistaken) that there was a convention/rule that inflight announcements be in at least the language of the originating and destination ports for the segment or flight.

I have found that this as a minimum on every flight I have been on with every airline.

So the Mandarin only really needs to occur on flights in and out of officially speaking Mandarin speaking ports (China mainland/Taiwan).

I wouldn't expect it HKG to almost anywhere else.