I feel like probably the language they were speaking was Japanese, since why would you /not/ have them speaking Japanese?
I am clueless and do not speak Japanese.
From what I heard, people were speaking Japanese, but I couldn’t clearly hear the background people in the various scenes. However, I think the movie takes place in something like a Japanese Hong Kong or Japanese Singapore, probably following a world war which shuffled the national boundaries throughout Asia.
Note: “Ghost in the Shell 2017 takes place in Japanese Hong Kong” is speculation on my part. However, some of it was filmed in actual Hong Kong, so it’s not entirely off-base.
It just sounds like the most credible explanation for why “Japan” is suddenly so multiracial, multicultural, and English-speaking that an entire team from its internal security services consists primarily of non-Japanese people who speak English.