How do you know when you're at the stage that you should start having classes purely in the target language?
I'm teaching a student from A0 level, only in English. If the student wishes to translate, then that can be done in his/her own time.
I've also started classes in a new language at A1 level, and I try to use only the target language in class. I hate resorting to this crutch called English. Again, any translation or English-language explanations can be done on my own time. Classes mean your time and your money, so better make the best use of them!
If you want to swim, you get in the water, don't you?
At A2 level.