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Catalan Language in Spain (& France)
Catalan is spoken in Catalonia, Valencia, the Balaeric Islands, some parts of south-east France and the country of Andorra. About seven million people speak the language. Catalan is intelligible when written down if you speak Spanish (and/or French) but the pronunciation is quite different.
Basque Language in Spain (& France)
The Basque language is spoken in the Basque Country and Navarra, as well as some parts of south-west France. Approximately one million people speak the language. It is completely different to any other language you will have heard before.
Galician Language in Spain
Galician is spoken in Galicia, with variant called Eonavian spoken in Asturias. Approximately three million people speak the language. It is the closest to Spanish of the three regional languages in Spain - if you also speak a little Portuguese, you should have no problem understanding the language.
Attitudes Towards (Castillian) Spanish in Catalan, Basque & Galician Regions
Genuine hostility to Spanish speakers is rare and even rarer when it is a tourist who is genuinely trying to speak the language, but mild animosity is not unheard of. It is often said that a Basque or Catalan would rather you spoke English to them than Spanish. If you meet such a hostile person, you have to ask yourself if you really want to be speaking to them at all!
Despite the notoriety of Basque separatists and the violent means they take to make their point, I've always found the Catalans to be the most fervently nationalist of the Spanish regions. Street names are written in both Spanish and Basque in the Basque country, whereas in Catalonia they are only in Catalan. Confusingly, Spanish speakers in Catalonia will often call Catalan street names by their Spanish equivalent, which can be quite frustrating when you're searching for it on a map!
It is pretty much unheard of for Galicians to resent the use of Castillian Spanish in Galicia.
Spanish (or Castillian, as purists call it) is spoken in all but the most remote villages in these regions. You don't need to learn any of these languages, but learning the phrases on the following page will definitely be appreciated.