How do they teach then? Are they teaching students who already have some English knowledge? Your friends are helping them improve, instead of teaching from scratch? Its understandable if thats the case.
I haven't taught a second language myself, but I am around a few people who teach or have taught languages, and I've picked up on it a bit.
Check the left hand side for the forums, there's volumes of information on just about any question you could ask.
Tealit.com is good for Taiwan.
Of course, the people teaching English without knowing any of the local language would claim everything is alright.
But it's undeniable that teaching will be more efficient if you do know some of the local language too.