Some silly person started cooked up a bizarre story that many people seem to take as fact. "A long time ago," it starts, "there was a Spanish king who spoke with a lisp. To make him feel better, everyone spoke with a lisp also. And that's why 'Barcelona' is pronounced 'Barthelona'."
Yike! Where does one start? It's only the "c" and the "z" that are pronounced as "th" in Castilian – an "s" is still an "s". The other, tiny, insignificant little issue is that in Barcelona (and the rest of Catalunya) the language is not Spanish, but Catalan. And besides, few people in Catalunya has ever tried to make the king of Spain feel better about anything. They see themselves as a separate nation. That hackneyed, old story can be dismissed as pure myth-understanding.
Catalan is a romance language, like French or Spanish. In other words, it's descended from Latin. Its closest relative is Provençal, which is spoken in the south of France. Catalan is part medieval, part quite-different, and definitely not a dialect of any other language. It's always been distinct, and Catalans were some of the first people to drop Latin and use the vernacular. Tirant lo Blanc, considered to be the first modern European novel, was written in Catalan.
Catalunya was a major seafaring nation, and in the Middle Ages, the use of Catalan was second only to Arabic in the Mediterranean. It's still spoken in modern-day Sardinia (the result of conquest), and even appears on signs. Other conquests, by the way, included Corsica, Sicily and Albania (though they soon left Albania because they didn't know what to do once they had it.)
After the integration of Catalunya into Spain, the Catalans still spoke their language, but were under pressure to pick up Castilian. While they did pick up Castilian, they never dropped Catalan. The lowest point came recently, when Franco tried to ban Catalan altogether. It was still spoken at home, and needless to say, when the old Caudillo finally croaked there was a lot of dancing in Barcelona.
The Catalans have always regarded their language as part of their identity, and that's why it's held on so stubbornly. When Gaudí was introduced to the king of Spain, he spoke to the king in Catalan. He proved a point, even if the king didn't get it. Nowadays, some Catalans prefer to speak English with foreigners rather than Spanish, which they know perfectly. Again, a point.
Catalan has a unique phonology. It preserves the "f" from Latin, where Spanish changes it to "h". "Horno" in Spanish is "forn" in Catalan (like the English word "furnace"), and bakery signs all over Barcelona say "forn de pa". Where Spanish words end either with a vowel or the consonants "n", "l" or "r", Catalan words end with any consonant they choose, mainly because final vowels have been dropped.
The telltale giveaway of Catalan is the consonants, which seem to have more voicing. The plural definite article, "els" is pronounced "ellllzzzz", with a hearty "l" that makes you worry the speaker is swallowing their tongue. There are various pronunciations of the "ll" sound, which, as in Spanish, is pronounced like the letter "y". It sounds simple enough, but when one of these is in front of an "s", all bets are off. Only a native Catalan would even attempt it.
Finally, the "j" sound sounds like a "j", as in "jar". There's a Catalan tongue twister that goes:
Setze jutges d'un jutjat mengen fetge d'un penjat
Sixteen judges on a tribunal eat the liver of a hanged man.
This promethian epic must be the most succinct ever composed in any language, but you have to admire its lyricism. It was so inspirational that there was a group of musicians from the 70's who called themselves Setze Jutges (who sang in Catalan despite the prohibition). There are a lot of very earthy and entertaining little proverbs in Catalan, some of them a little raucous. Robert Hughes gives a very good account in his book, Barcelona, which is excellent reading in any case.
A good illustration is the local versions of all the biblical names. Jordi is George, the patron saint of Barcelona. At least 109% of male Catalans seem to have this name. Joan is John (no, Joan Miró wasn't a woman!), Antoni is Anthony, Josep is Joseph, though the kicker (to my mind) is Lluís.
At this point people are totally bilingual in Catalan and Spanish. Because the two languages are so related, linguists have found Catalan bilingualism an interesting study. Where Spanglish combines two very distinct languages, in Catalan and Spanish it's easy to borrow without knowing that you've done it. And the languages are so close in daily use that it's interesting to observe how and when people switch.
When I got to Barcelona I was delighted that people spoke to me in Catalan, and was more delighted still when I understood most of what they were saying. I've always though that Catalan sounds really cool. I kept asking my friend Jordi to teach me Catalan, but he kept insisting that I should learn something practical like French. (Why learn German, goes the same argument, if the Germans speak such good English? You can read everything in translation!)
I suppose he's right, but it's a crime that there's not enough time in the world for all of the interesting things, or that my brain isn't big enough to fit it all into the time allotted. If either of those objects suddenly become moveable, I can see a potential project.