I think Duolingo is great for exactly that kind of situation, where multiple languages exist in one country, and that is actually the norm, rather than the exce

I think Duolingo is great for exactly that kind of situation, where multiple languages exist in one country, and that is actually the norm, rather than the exception. For example there is also a course in the incubator teaching Catalonian for Spanish speakers, Catalonian being a language spoken in a part of southern Spain.