I don't care what language you speak, please don't ever tell me you don't need to study another one. Unless you want to start a fight. Then you've found one.
And if your teacher ever asks you whether you (as a Japanese student) should study English then you should answer yes. Always. Even if you disagree because if your teacher has decided to devote their life to teaching you that subject then they probably aren't going to like it if you tell them it's a waste of your time.
The foreigner and native English speaker who has to grade your papers also doesn't appreciate comments like "Japan better culture has than English." No one who wrote "I agree, I think we need not study English" got an A this week except the kid who thought that "English liking students should study English and Chinese liking students should study Chinese." He didn't like not having a choice, which I totally get.
Not valid reasons for not wanting to study a foreign language:
1. It's hard.
2. Other people should just learn English/Japanese/other (This is especially absurd when you think that Japan is the ONLY country that speaks Japanese and it's not an especially big country.)
3. I'm never going to leave the country anyway. (Way to think big!)
4. "If I speak with a foreigner I will use gesture." (Good luck with that! And I hope you don't have a yeast infection!)
This isn't to say that I don't think foreigners in Japan shouldn't learn Japanese, because it certainly does make your life easier. And foreigners in America should also learn English for the same reason. In fact learning English makes your life pretty easy no matter where you go because it is the international language thanks to British imperialism and American economic power after WWII, BUT just because touristy places will certainly have some English speakers doesn't mean your life won't be easier if you learn some basics.
Learn a language. Make a friend. Visit new and exciting places. The end.
/steps off soap box