Pelayo

I know there already are a lot of VT tips on the Catalan language, but as a translator and language lover, I have found most of them unexact or incomplete. So, I'll try to write my own tip. Here, I will only deal with the language itself, leaving my opinions about Catalunya's linguistic policy for another tip.

First of all, Català is a Latin language: it is not a dialect, a patois or any variant of Spanish. It has its own grammar, pronunciation, vocabulary.
As for the pronunciation, I have found it more similar to Portuguese than to Spanish, due to its intermediate vowels: e.g. unstressed a's are pronounced halfway between /a/ and /e/, while unstressed o's are pronounced like /u/.
Ortography makes it closer to Latin and French than to Spanish, while many words are very similar to their Italian equivalents.
Article 3 of the Spanish constitution allows the autonomies (autonomías or comunidades autonomas) to have their own official language. However, what makes Catalan far more important than Basque or Galician is its transnational dimension. Beside being the official language of Catalunya, the Baleares isles, Valencia, it is also the official language of the Principat d'Andorra. Moreover, it is spoken in Southern France (Perpignan) and in Alghero, a town in Sardinia (Italia).
This makes 9 million speakers, more than many national languages in Europe.

Like many European languages, Catalan has its varieties and dialects and varieties, as you can read here. However, I suppose that all Catalan speakers understand each other.

If you want to learn Català, you won't easily find many books in Spanish. Being the official language, everybody learns it as a child, so courses in Spanish are rare. I found one in a bookshop, titled Catalán para dummies published by Granica. It is a basic course including a CD and I think it's enough to get started.
A more complete Catalan course is published by ASSIMIL, my favourite language course publisher. There is an edition in Spanish available (El catalán sin esfuerzo) and one in French that will appear in 2009.