Your use of international school students learning chinese in Mandarin is not relevant.
Note that Mandarin is second language to international school.
More, your using Singapore is with the same flaw.
Chinese is second language to most younger Singaporeans.
Hong Kong is another issue.
Cantonese is mother tongue to most people.
I do not see how you see these cases can be interrelated.
PS I have no stand as to whether local student should learn chinese in mandarin to cantonese. I was merely correcting some of your flawed arguments.