http://screenrant.com/ghost-shell-movie-casting-controversy-international/
?There [are] all sorts of people and nationalities in the world in Ghost in the Shell. We?re utilizing people from all over the world. ? There?s Japanese in it. There?s Chinese in it. There?s English in it. There?s Americans in it.?[\quote]
My guess is while the film is set in unidentified asian metropolis Section 9 itself is an international taskforce under Interpol, UN or other umbrella organisation.