Interesting, thanks for that post above. I have been convinced for some time that there isn't a "rule" per se, anyone who flies CX around enough can tell you that you can be on the exact same route and get announcements in different languages (usually whether or not to include Mandarin)! I can think of two HKG-JFK flights last month....one they announced in Mandarin (3 languages), one only in the standard 2 (English/Cantonese). I suspect that maybe pre-flight a good ISM would check loads and see if there are a lot of mainland/Taiwanese last names, which generally have tell-tale English spellings vs. HK English-name spellings. If they see a sufficient # of last names like Wang, Li, Chen, etc. then include Mandarin as well.