Twitter has released a Spanish version of its site this week, and made the announcement in Spanish on its blog.
Before this, the only languages that were available were English and Japanese. But that didn't stop tons of users already tweeting in Spanish, like my colleague Daniel Shoer Roth (@danielshoerroth) who writes for El Nuevo Herald. (And thanks to Daniel for the heads up on this news.) Twitter said it is seeking the help of volunteers to translate its site in more languages.
To change the language, go to Settings and then scroll down to the drop-down menu for Language.