Pretty incredible. You, dear non-Catalan reader, might think it's much ado about nothing, really, how much difference is there between "Plaça Catalunya" and "Plaza de Cataluña"? Who cares? But there are very large issues here, which I hope to address one by one.
First, the names of streets, squares, and roads are all in Catalan in Catalonia. If you're looking for a street, the only street sign you will find will be in Catalan. Google Maps won't do a fat lot of good to you if it's giving you a translation into Spanish. For example, one of the streets near my apartment is “Carrer de Sant Domènec" (or Saint Dominic street) but Google has it labeled as "Calle de San Domingo".

(Then, there's the added weirdness that you can't actually say "San Domingo", it would be "Santo Domingo".) There are many, many other bizarre translations. Things like "Verga María" [Cock Mary] (and I don't mean roosters) for "Verge Maria" [Virgin Mary]. Or changing the name of the town, “Sant Boi de Llobregat” into "San Baudillo de Llobregat".
Think it won't matter, that Catalan and Spanish are "close enough"? Try "Calle del Oxidado" instead of "Carrer Rovellat". Or "Rambla de la Colina" instead of "Rambla del Turó". Let's just say I wouldn't rely on Google Maps to get around Catalonia any more.

Vilaweb was finally able to get a first explanation from Google Spain about the problem. “The problem has to do with a database that was supplied by a third party and the technicians are working on updating it."
Ultimately, to Catalans who are continually feeling mistreated by the Spanish government, who will not stand up for the Catalan language in Spain, the European parliament or anywhere else, it feels like a crass political move by Google. Perhaps it's just a technical error, but I just don't have that faith anymore.
Interesting that names in English have not been translated into Spanish, as in Plaça John Lennon, which turned into "Plaza John Lennon" but not "Plaza Juan Lennon".
Check into Twitter and follow #googlecat to see egregious examples and anger. Follow Vilaweb for the latest news.