add on to BB
JET and Nova (en.wikipedia.org/wiki/Nova) are the biggest con masters in this scheme. It's a lot of varying experiences but do note that Japan has a reputation of "Mcdonaldfying English". Just a few years ago, there was a whole lot of scandal kicked up about one of these countries not paying their teachers for 3 months etc.
And if you want to do it legit way, you might want to consider first getting a Teaching English as Second Language (TESOL) cert first. Most legit companies will make you take it or want you to have that before sending you out.
Either or, the less than legit will try to con your money by asking you to pay for your lessons before you even get to travel.