I hesitate to write about this topic. Probably any Japanese English teacher doesn't want to. But in the hope of helping Japanese teachers to think again about their own duty and responsibility, I'll write (under correction). I hope any reader won't be offended because I write this.
Though it sounds reasonable...
One of the saddest things in English language teaching in Japan is that a great number of Japanese English teachers teach English in Japanese and even those unqualified people could get a teacher's license.
Japanese often complain that they can't speak English or write it properly although they have studied it more than six years (in the case of a university graduate, he or she has studied it ten years! ). It's no wonder, however, they can't speak or write English properly, because what they did at school was nothing but loading themselves up with small things and facts about English, mostly for examinations (for mid-term or final examinations or university entrance examinations). And the teachers themselves weren't good at conversational English. It would be a miracle if Japanese could have become fluent English speakers after studying with these unqualified teachers.
However, it's sheer nonsense that Japanese English teachers keep talking in Japanese all through English classes. Why? Children start to use their mother tongue before they know anything at all about its grammar. That is, children learn to speak their language by speaking it. It's very clear that the best way to learn a foreign language is being exposed to it and using it as much as possible.
Putting Japan's defective English language teaching system aside, how can ordinary Japanese children learn to speak a foreign language from the teacher who doesn't or can't speak it? It must be really frustrating for Japanese English teachers to speak only English all through the class. I sympathize with Japanese English teachers (first of all, I sympathize with myself!); they themselves studied English with Japanese professors who weren't fluent English speakers. Japanese English teachers will say that it's easier for them to speak Japanese and it's more comfortable when they are speaking it. Without doubt. Personally I'm most comfortable when I'm speaking Japanese. There is no fear of giving myself away as long as I'm speaking my mother tongue. And there is no fear of suffering from feelings of inferiority as long as I'm using it. I know well that I can't come near the native (born) English speaker when it comes to English.
A clever deception is...
I know I shouldn't try to defend myself by saying things like this, since it's a clever deception. What am I? I'm a Japanese English teacher who is earning money by teaching English to Japanese university students. That is to say, I shouldn't remain in Japanese to make it easier for myself. My task is to help students to be able to use English as a means of everyday communication; many of my students actually want to get a job where English is required. And I mustn't forget my English-speaking colleagues (particularly, those who haven't acquired ｃｏｎｖｅｒｓａｔｉｏｎａｌ Japanese yet). Lack of communication between Japanese teachers and non-Japanese teachers often occurs when they don't try to communicate by speaking the same language.
Suppose that there are ten Japanese English teachers and one native (born) Ｅｎｇｌｉｓｈ speaker in a school or university and the Japanese English speakers don't speak English at all when they are in the same room for a meeting. The English-speaking person will most probably feel left out. Then, he or she might propose that they speak English when they are with him or her, saying that using only Japanese clearly excludes him or her from taking part in the schoolwork and wastes his or her time; he or she isn't given any voice in decisions and discussions which should be his or her right as a member of the teaching staff. This is the sort of frustration which builds up in him or her.
Not to cut off any native (born) English speaker, Japanese English teachers should promote friendship and make every effort to maintain good relations with them. All of them are human beings as the Japanese. They have every right to be treated fairly and humanely.
At hand I have an anonymous letter written by a John Doe [or a Jane Doe], laughing scornfully at his (or her) Japanese colleagues' inability to communicate in English. And the letter is full of insinuating and resentful remarks. It had been dropped in my university mailbox (and in some other people's mailboxes). I don't know who could have done this sort of thing, but I think I ｃａｎ understand his or her feelings very well. The writer must have always felt that his or her feelings or opinions were totally disregarded. The person targeted at in the letter must have forgotten to promote friendship and make an effort to maintain good relations with the person who wrote the anonymous letter, or he or she must have failed to succeed in dealing properly with non-Japanese teachers.You can laugh this away as childish. However, you shouldn't ignore the fact that the writer despises Japanese English teachers for their incompetence in using English. The writer also points out that there is a big gap between a professor's title and his or her real ability in Japan. Anyway it shows that some kind of resentment against his or her unfair treatment must have created a most difficult barrier for communicating well between Japanese teachers and him or her. This sort of thing is really bad.
To brush up on your English
More and more Japanese English teachers are becoming good English speakers and part of them have native fluency and another part of them have near native fluency. Quite a few Japanese teachers, however, speak poor English, nor they can use ｐｒｏｐｅｒ level of speech. To improve their English, there is no better way than using it themselves in everyday classwork or conversation.
It's tragic for Japanese students to have to study English with Japanese teachers who don't (try to) or can't speak English. It's even a crime to (try to) teach facts about English all through the class.