Hi Yassine,
I think here it's best to avoid the literal sense of تناوب. The approach described in your text sounds like the language immersion programs at some schools in the U.S., where students learn a second (or third) language by using the new language to study other subjects such as math or history. The teacher presents a normal math lesson, for instance, but in a foreign language such as French or Chinese.

From Wikipedia: Language immersion, or simply immersion, is a technique used in bilingual language education in which two languages are used for instruction in a variety of topics, including math, science, or social studies.