I've noticed lately that many questions get migrated from SO to other sites or get closed for various reasons (e.g. they're duplicates or off-topic). It made me wonder how migration is possible. I assume that a request to migrate a question has to be confirmed by an admin of the target site. Is that so? Can someone share how it works?
Migration does not require confirmation from the target site. However, mods on the site do get to see a list of recently migrated questions.
It's entirely reasonable that a migrated question will be a dupe of an existing question on the new site. Users on the original site might not be aware of this. This process is working exactly as it should.
Other times, users on the original site may not realize that the question is not exactly on topic for the target site. In these cases the question probably doesn't belong anywhere, and will just die quietly.
I was about to post the following as a Question but since it would have been a near duplicate of this one I will try to phrase it as an Answer instead.
I think the best mechanism for migration would be if questions can be nominated by high rep users from either the posted or target site, and then the question nominated for migration gets reviewed by high rep users at the opposite site prior to the migration occurring.
In other words, I'd like to see more push and pull of questions between sites, to make them become (more) on-topic at the target site, and to facilitate easier migration via the review queues at both ends.