This is a Swedish children’s tape. Its title, “Den hemlighetsfulla ön”, translates as “The mysterious island”, but the text on this cover clearly refers to Deux ans de vacances:
Here you can listen to a story about fourteen boys who by an accident are cast upon an unhabitated island. During an entire summer holiday they have to manage themselves. Where do we sleep, what do we eat. The boys can manage in spite of all difficulties. It is a really different summer holiday.
I bought this tape at a very small flea market near a very small village, Näs Bruk, in Sweden.