It is, but in Spain's case it is sometimes nationalism too, as the Spanish Crown rules over several different old independent kingdoms which have cultural differences and languages that stem directly from Latin (ex. Euskera).

I don't know where academics put the bar, but in my mind any area that has its own non-dialect language or was once an independent entity for a good while can claim to be a nation. Though not sure what the claim would mean in practice.

That said, I'd rather see all these things die down and have a strong EU of federated states of whichever size helps democratic and economic progress. Tall order, I know.