I can only speak for my 2-week experience of travelling Japan alone (and my Japan-fandom), however I also heard some stuff about China.
First, Japan. Most people there have problems speaking English and you will have sever trouble communicating, even though they started incorporating English words into modern Japanese. I have seen malls of shop clerks and policemen and station employees unable to speak a sentence of English. Your best bet are students, they are fairly good. If you need to find an English speaker urgently, go to a bar or 7-11 or Karaoke in the early evening. Chances are high that you will find a part-timer there :) Restaurants in the evening might also serve food to businessmen, who are able to speak English, but you shouldn't disturb their meal ;) All in all, I was really glad that I speak A2 level Japanese, although that is not much at all!
As for China, a Chinese friend of mine told me that there are a lot of people who are good at English, because the Chinese are diligent and study hard, and English is one of the subjects. However, again, you will have the best chances to speak English with students and young (academic) people. Many Chinese have the opinion, that a Chinese dialect should be the lingua franca, as most people in the world are Chinese. As far as I know, Hong Kong uses English as an official language (it was once a British colony). Though it does not directly belong to China, you might use it as a starting point for your China-experience. It might lessen the cultural shock.
Oh, btw, don't underestimate cultural shock. I have been to a few countries, yet, Hungary included. For me as a German, many things which seemed similar at first time out quite different (especially some social behaviors), and I was fortunate that I had the chance to work there and talk to my colleagues :D However, compared to that, Asian countries, like India, China, Japan, etc., are very different and you can easily do something wrong. Just as an example: you should not stab your rice with your chop-sticks when in Japan, as that's only done with the rice for deceased people. Also, you should mute your phone when riding a train or bus (also no vibration) and restrain from talking or being loud, since that's considered rude. Finding a guide or friend over there to explain subtle behaviors will definitely help you!
Since Team Hashnode is located in India, I am pretty sure that they can tell you a bit about English there! Fazle Sandeep Sai