"Japanese businessmen usually bow to *each [other] ^in Japan." *We use the pronoun "each other" to indicate reciprocal interactions where each person in a group does something to someone else and receives a similar action from the other party. ^ I am not sure if you are referring to the social etiquette of Japanese businessmen only when they are in Japan. If this is indeed your meaning, feel free to include "in Japan". However, if you are focusing only on the social etiquette of Japanese businessmen (regardless of where they are), "in Japan" would be redundant – "Japanese businessmen usually bow to each other." Your choice depends on what you want to convey.

"Japanese businessmen usually bow to each other in Japan."