Japanese, of course. Signs, menus and maps are written in Japanese, which uses a combination of three writing systems. Hirigana (ひらがな) is used for native Japanese words, katakana (カタカナ) is used for foreign words, and kanji (漢字) are borrowed Chinese characters. I used my basic knowledge of Japanese language daily to do everyday errands such as grocery shopping. However, one thing I did not expect was how keigo, honorific, formal Japanese speech, was frequently used in casual situations. Announcements for train schedules were given in keigo, and shop staff speak to customers in keigo as a gesture of respect for their customer's patronage. A phrase you'll often hear shouted when entering a store is "irasshaimase!" It means "Welcome [to our store]!" and while you are not expected to respond to "welcome," it is common to do pekori, a quick single slight bow of your head.
Although Japanese people study English as a subject from middle school to high school, many are not fluent since they rarely need to use it in Japan. Some are very shy to speak it but will try their best to help you if they know you're not fluent in Japanese.
