Ведь учителя должны знать не только

Ведь учителя должны знать не только язык, но и как научить языку других, а для этого нужно самому знать материал безупречно

Результаты (английский) 1:

After all, teachers must know not only the language but also how to teach the language of the other, and to do that you need to know the material perfectly

Результаты (английский) 2:

After all, teachers need to know not only the language but also how to teach the language of the other, and for this you need to know the material perfectly

Результаты (английский) 3:

because the teachers have to know not only the language, but also to teach the language of the other, and this need to know the material perfection