Gary Illyes from Google said on Mastodon this morning that you should 301 redirect URLs when there is a "close-to 1:1 match" for that URL. We know that, but what he added was this is even true for when the "language of the content doesn't match."
Gary wrote, "301s are great when you have at least a close-to 1:1 match for the URL and you want to consolidate them, perhaps even if the language of the content doesn't match. 404s for everything else. But that could be just me; I love deleting stuff."
So if you have a close 1:1 match on URL A and URL B, even if URL A is in French and URL B is in English, you can 301 redirect them. I suspect this sometimes happens when you decide to pull out of a region and no longer need to translate specific pages.
If you think of how localization works and hreflang works, this advice from Gary makes sense. I mean, hreflang is not a ranking thing, Google said numerous times. It just helps Google understand that this page in English is the same page as this French page but just in a different language.
So it may make sense to 301 redirect those pages even if they are not in the same language if those pages are going away.
Forum discussion at Mastodon.