Although there are a significant number of multinational corporations (MNCs) in Japan as local entities or subsidiaries, limited research has been done regarding language and style changes by Japanese managers working at MNCs’ subsidiaries. The Japanese managers normally communicate with Westerners (mostly Americans in this research) at or from headquarters (HQs) in English, while they need to communicate with their local superiors in Japanese. The Japanese managers need to switch not only languages, but also discourse styles, because styles of communication between Westerners and Japanese are different. Nevertheless, limited research has been done regarding how and to what extent the Japanese managers working at MNCs’ subsidiaries switch languages and discourse styles, and the implications of the switching for communication with their interlocutors. Communication Accommodation Theory (CAT) explains various aspects of discourse between people and groups, which can be useful for understanding and explaining the language and discourse style switching by the Japanese managers working at MNCs. Clear differences of communication styles of MNCs’ subsidiary managers were identified through questionnaires to them. Further analysis of data and interview results revealed linguistic and cultural accommodation trends by the Japanese managers working at MNCs.