Saints and sinners all agree
Spanish is a lovin’ tongue
But she never spoke Spanish to me
In addition to the option that sets the language to use for the front page of your blog, each user will be able to choose the language they want to use for the admin interface. If your blog is Spanish but you want to use English in the admin interface, you can do that. Each user gets to choose the language they want to see in the admin.
This isn’t yet live on wordpress.com but should be soon. If you use wordpress.com and want to help with translation, head over to translate.wordpress.com and translate a few strings. This will help other wordpress.com users as well as the WordPress and bbPress communities in general.
Update: Spanish is now active. Not all themes have been translated, but the admin area has good coverage. If you don’t want your admin to display in Spanish, visit your profile and change the Interface Language (Idioma de la interface).