Texy! provides typographic quotes for several languages but currently this is a system-wide setting affecting all content. Since Drupal 6 has i18n features built-in it might be feasible to link this setting to the post's language instead of a global setting.

I personally don't see much use for typographic quotes that are wrong for half the posts on my site :-(

Maybe make it an option in the UI for people that want to keep a site-wide behaviour.