I've taken one idea from the only comment my previous post got, and am in the process of implementing another idea I had thanks to finding multi-language versions of the Inverloch webcomic.
I've only converted pages 1 and 2 to include Spanish support, but as that may imply to the astute out there the previously-linked-to example interface now supports changing the language of the comic dynamically using overlays. I also added a small text-blurb at the end of the page to explain how to change pages in what is (I hope) a clear and simple fashion.
Unfortunately I'm still grappling with the best way to implement the textual navigation side-bars and footer to support multi-language support. It'll involve some re-engineering of the overall engine, but the core structure shouldn't change that much. I need to re-test the new version on Safari, but it still works on IE6, O9, FF1.5, and K3.5.x so I'm confident I haven't broken anything yet.