Just finished quite a bit of code tracing to figure out why accents are stripped from permalinks in wordpress. It all boils down to a sanitize_title filter (the function is sanitize_title_with_dashes) which calls remove_accents. I created a plugin which removes the ‘dashes’ function and replaces it with the same code except it doesnt call remove_accents.
Edit: Sorry. This file is no longer available!
Download PermalinksWithAccents Plugin