it can make students confused by the time they do not know which language will prevail during the lessons.

it can make teachers' work worthless, as they will not need to be fluent in the foreign language.

the use of L1 has proved to be completely useless in a foreign language classroom.

by exposing students to the authentic language all the time, they will learn it somehow, even though they do not understand anything during the lessons.

since students are there to learn a foreign language, they cannot use it successfully if they still rely on their L1.