The strategy in which school subjects are taught in both the learner's original language and the second (majority) language is called:

biligual schooling

Explanation:

Bilingual schooling involves teaching educational programs in the learners' native language as well as in the target language. There are several bilingual schooling systems which teach contents in both first and second language. For instance, Dual Language Immersion includes native speakers and non-native speakers receiving content in both languages, while Transitional Bilingual Education involves teaching content in the leaners' native language during the first years, and gradually switching to the target language.