Background info: People want to tag their music using unofficial titles because they can't read the original titles. To make this possible, we added pseudo-release as a release status and a relationship between the two. However, since Picard doesn't use the links between official and pseudo-releases, we have to duplicate all the data the user is interested in tagging with, which means editors either need to edit the same thing twice or leave the data inconsistent. That is clearly not ideal, but there is some opposition to reducing the amount of duplicated data while there is no way for Picard to fetch the data from the official release.

What we need is a way to use data from one release while tagging with the titles from another. I suppose it probably depends how we want to implement this, so I won't split it into multiple tickets yet but there are several scenarios:
1) A pseudo-release is loaded - we want to fetch the release/relationship info from the official release automatically.
2) An official release is loaded - we want to fetch the tracklist info from the pseudo-release automatically.
3) The user is not happy with the selected official release and wants to change it (e.g. wrong date or cover art).
4) The user is not happy with the selected pseudo-release and wants to change it (e.g. wrong language).
5) The user has loaded a previously tagged release into Picard and expects it to load the same information they originally tagged it with.

For 1) we can probably just pick one of the linked official releases and select that one in the "other versions" menu. Then for 3) the user can select a different official release using that menu.
For 2), I think some kind of language preferences would have to be involved. There are western releases which have Japanese pseudo-releases and Japanese releases which have Latin pseudo-releases, so simply having a checkbox saying "use pseudo-releases" would produce strange results.
For 4), a menu similar to "other versions" but for languages would work.
For 5), I'm really not sure what we can do here other than write multiple release MBIDs to the files.