To close the loop here, @mqmenchaca and myself worked on this at the same time without knowledge of the other working on it. And came up with PRs just a few hours apart! I had already merged my PR to core just before seeing Max’s, so sadly we can’t merge his work in core. Very much appreciate the contribution nonetheless, @mqmenchaca!
The commit that adds this feature is this one: DEV: Add a rake task to export/import translation overrides (#18487) · discourse/discourse@4d80110 · GitHub
To export, run bin/rake export:translation_overrides (it will create a JSON file with the overrides).
To import in a separate instance, copy the exported JSON file there and run bin/rake import:file["filename"].