To politely say "Please bring the textbook" in Japanese, you can use 教科書を持ってきてください (Kyoukasho o motte kite kudasai), which directly translates to "Please bring the textbook." This phrase is polite and suitable for formal or academic settings. In a more casual context, you can say 教科書を持ってきてね (Kyoukasho o motte kite ne), which carries the same meaning but is less formal and friendly. Both versions are commonly used to request someone to bring a textbook to class, a meeting, or another relevant situation.