if I have a single that is available in English & Spanish, how do you edit the title for the non default language?
Things changed with Craft 2.2:
Single sections’ Entry Types now have “Show the Title field?”, “Title Field Label”, and “Title Format” settings.
...and yes, the Title field is translatable of course!
Single titles are not translatable in the control panel since Craft version 2, they need to be set in your translations file.
Apparently, the ability to localize Single Titles in the CP is coming back in 2.2. twitter.com/ademers/status/490205315934470144 Aug 27, 2014 at 17:02
entry.title isn't displayed in the entries section of the Control Panel anyways, so (currently) there's no way to edit it even for the primary locale.
If you want the title to be user-editable, what about adding an additional field
In case this is a one time config (done by the admin), you could use the
translation filter like @PatrickNesbitt mentioned or edit the title for all your locales in the
craft_content table in the DB.