At the moment, my solution is to never work with the relation starting from the non-localized content type.
So the direction of the relation should always be from the localized content type to the non-localized content type, or of course, just not localize both or localize both.
In some cases, I found that turning off the internationalization for one content type made the direction of the relation always be from the localized to the non-localized in my data structure. So it was more of a content type design problem in my case.