Mirandese, or none.
Now serious, most european countries have more then one language. We look at the UK and we see gaelic, scots and others, we look at Spain and they have Basque, catalunian, galician... Why should we eliminate so much culture? These languages are part of the local populations identity, let it be like they are, we should be working on protecting these languages, not eliminate a lot more of national languages.
Still, the need for a language with more range exist, i think that English can fulfill that role, but at the cust of eleminating national, or local languages.