I’ve just seen the film and there was one thing I really didn’t like: the use of languages. There were conversations where one character was speaking one language and the other character another. I would have preferred the Hunt for Red October method where they started with everyone speaking Russian (or Japanese in the case of GitS) then transitioned to everyone speaking English.
Beat Takeshi never seems to speak English even in American productions. I assume he just doesn’t speak it very well, which is why he usually ends up playing bigwig Japanese types with low BS tolerances (see also: Johnny Mnemonic).
As for Watsonian explanations, I just assume his speaking exclusively Japanese is another indicator of Aramaki being part of the old guard. In contrast to his subordinates (and antagonists) who are various degrees of cybernetically enhanced, multilingual, multiethnic, and multinational operatives (and Togusa), The Old Man is a gruff old take-no-shit revolver-wielding government man who speaks only Japanese and doesn’t let technology be a hinderance or a crutch.
And judging by the ease with which he was able to bring the Prime Minister around to his side despite Cutter being so confident of having the government in his pocket, Arimaki probably knows where most of the bodies are buried too, in order to pull those kinds of strings.
A visually spectacular (IMAX 3D), tolerable narrative, anime construct with Scarlett Johansson in a weirdly sexy unitard. All thumbs up here.