If you're flying in C or F maybe the FA has time to look at the manifest to decide which language to speak to you in but in Y English would be the first preferred language. Obviously SQ is Singaporean so English is primary, but it happens on other Asian carriers too. CX is also English-first, and I see FAs almost always talk to passengers in English before Cantonese. And HK isn't nearly as English-proficient as Singapore. On Asian UA flights where the vast majority of FAs speak English as their second language, they still speak English first because it's an American carrier. (And the pursers almost universally have serious difficulties making announcements in English)

I think those are the only 3 Asian carriers which favour English though.

I know many Chinese Singaporeans who speak English at home despite being fluent in Mandarin/Minnan.