There is no such thing as International Standard English. I have been affiliated with many EFL organizations over the years, and every organization (school) has always leaned towards either American English or British English. My present university in China has tried to pretend this problem doesn't exist, and I feel it has led to bad feelings all around. When a class has an American teacher at 8 am, an English ("London") teacher at 10 am, and a Scottish teacher at one-thirty, and everyone says there is no difference, this is doing a great disservice to the students.
A good EFL speaker will be comfortable in both American English and British English. A speaker who speaks a mish-mash of both sounds terrible.
A Chinese person who comes to America and only speaks British English comes across as being rather odd. And a Chinese person who comes to America and doesn't know the American equivalent for "go on holiday" sounds both odd and uneducated.

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