This article presents the results of a 3-month empirical study in a private minority school of the non-profit association DIWAN in Brittany, France.The private minority schools of DIWAN, founded in 1977 as a reaction against monolingual language policy in France, were modeled on Canadian immersion schools, which first appeared in 1965 in Ontario, as well as on the Ikastolas (Basque country) and Welsh language schools (Wales). The network of DIWAN immersion schools, which has expanded over the years, has created a linguistic regime, ideologically founded in language revitalization. The regime guarantees a secure Breton-only space in schools, along with the teaching of two foreign languages (English and German or Spanish) and classes in the students' mother tongue French. This quite secure Breton-only space is definitely in opposition to a globalized and flexible world. In this context, questions such as "How do the pupils experience their multilingualism?" and "Do they encounter separated multilingualism?" arise.The empirical study combines language biographical (language portrayals and narrative interviews) and ethnographical approaches, as well as linguistic landscaping, and attempts to reveal answers to the questions above.