I think your best bet is to do a home stay or working holiday overseas, but failing that one on one classes would probably be your best option. A lot of group classes will be geared toward delivering what is considered the essentials of English language, i.e standard language that most English speakers will understand. You could also try watching movies in English (and subtitles in Japanese). Let me know if you have any other questions. I have a lot of experience teaching all kinds of classes
I don’t know what level your English currently is but I think you need to build up from a strong foundation first.
Some jokes are simple but humor can be very difficult to get until you understand the culture and the situation. I have lived in Japan for over twenty years but I often don’t understand Japanese jokes on tv.
I suggest you learn from a general English text and as you get better at English you will be able to speak more naturally and understand more and hopefully even be able to understand and use jokes.
If you have speaking practice your teacher will help you to speak more naturally. If you use the language to communicate it will be easier to remember it.
Good luck ✊
Daily English Conversational class is helpful to speak practical English, you can also learn some Idioms for some sorts of jokes. Watching English movies, with English subtitle (as you want), is also advisable to get some new expressions 😉
Watching TV series and movies or listening to music is great in English, however if you want to gain confidence speaking English the best thing to do is practice as much as you can! Let me know if you are interested in English conversation classes!