closing the information window you mentioned is not critical, but starting a new addlocale process before the old one has finished most likely screwed up things. In addition, the 'incomplete download' thingy will be fixed in the next addlocale version. For now, please try the following commands from a konsole:
su -c rm -f /es_ES.tar.bz2
2) run addlocale and select "English (US) [Select to restore default]", then reboot your system, all should be in English now.
3) run addlocale and select "Spanish" and proceed as usual
hope this helps, regards,