AnonymousWhich means, in the case of the Basques, it is the Spanish, mostly Castillano-speaking, immigrants into the Basque region who should have learned Basque, right?
It would make sense for them to learn the language, but it's not a necessity. And on top of that, if the group of people moving into a given region intend to (a) set up their own communities, (b) maintain their linguistic and cultural identities, (c) reject the host community's culture and language, and (d) not associate with the host community on a day-to-day basis, then it's not really worth the effort for most people.
The issue gets cloudy when we start to get into the intention of said 'immigrants'. Some would argue that the English were immigrants in North America. Others would draw a distinction and call them colonists. The idea that a piece of land is the determiner for which language should be spoken is also asinine. The factors that determine what language a person speaks ahould be economic and social.
So, to answer your question: Not if they decided that they don't want to participate in the Basque culture or economy.