Thanks to Santi Regueiro, Smart Archives has now been localized. He localized it for himself and then e-mailed me his modifications. Localization was probably the most requested feature and has been in the queue for a while. I kept putting it off because I thought that it would require a decent amount of time, but after looking at his changes I quickly realized that it's rather elementary and something I should have taken care of sooner.
After exchanging a few e-mails and making a few tweaks, the changes have been incorporated into the latest version, which should localize automagically. Please let me know if you run into any trouble.