The co-official languages of Spain are a mess. 
Firstly – euskara is spoken by nobody outside the three Basque provinces plus neighbouring Navarra (the Basques think that Pamplona should be their capital, but are stuck with Vitoria, or Vitoria-Gasteiz to be pedantic, which is at least in the right geographical location). All Basques will (and for practical reasons must) speak Spanish. You might get a word or two in Euskara to make the point, but, if nobody understands…
Then there’s galego, a mix of Portuguese and Spanish. There’s aragonés – or fabla – as well (it’s close to extinction apparently). Over to the East, the Catalans like to speak catalán (unless they live in Valencia, where it’s called valenciano). In Valencia, normally Partido Popular territory, they prefer to speak Spanish anyway, and they would no doubt prefer it if I said ‘castellano’. Indeed, castellano is more like the King’s English; it’s best spoken in Valladolid, while worst savaged in Cádiz.
Catalán has so much baggage, what with that Independence thing, that Miriam Nogueras, the parliamentary spokesperson for Junts del Catalunya, insists on making all her presentations in that language. Since nobody else in las cortes either likes her or cares what she is saying, few deputies bother to plug a pinganillo into their ear for the translation...
Since we got on this subject, I would suggest that el inglés is probably the fourth-spoken idioma in Spain – rising to second place during the summer months.
Having trodden on more than a few toes with the foregoing, I’ll note here that my friend José Antonio Sierra (who founded the Spanish Cultural Institute in Dublin, and served as Director and Cultural Manager of the Instituto Cervantes in Dublin for many years) has been campaigning in Andalucía to get the escuelas oficiales de idiomas, who merrily teach English, French and German, to offer courses in Spain’s minority languages, so far without success.