When the migration script hasn't run, going to http://developer-dev.mozilla.org/de/Farbverl%C3%A4ufe_in_CSS gives a 404. It should try to redirect to http://developer-dev.mozilla.org/de/docs/Farbverl%C3%A4ufe_in_CSS which may or may not give a 404.
I guess my question is... how can we know to redirect a not-yet-migrated page if it hasn't been migrated and we don't know it exists? The MindTouch locale redirect catch-all was built to only handle known-existing pages so as not to be overzealous in redirects. We could redirect /de/* to /de/docs/*, but there may be some point in the future (or that we've missed now) where something /de/ does *not* go to /de/docs/
Is this related to the #REDIRECT [[/url/here]] feature?
This seems like something no longer relevant now that all content is migrated. True?
Going to say this is resolved by virtue of migration being as complete as it's going to be.