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They speak español.

Castellano or Catalan, perhaps?

and also Basque (Euskara), Galego (Galician) and a maybe couple of other languages with a quite representative number of speakers.

There are five co-official languages recognized in the various regions of Spain: Castellano (everywhere), Aranese (Catalonia), Basque (Basque Country), Catalan (Catalonia), and Galician (Galicia).

In addition, there are several localized languages, that are not "official" but "recognized": Aragonese (Aragon), Asturian (Asturias), and Leonese (Castile and León).

And there are countless dialects of each.

For what is worth, Galician is essentially a variant of Portuguese, in the sense that it's mutually intelligible with European and Brazilian Portuguese. There are differences in pronunciation but not significantly more than between European and Brazilian Portuguese.