Thanks for the post. It seems like you are having issues migrating from Xcode 14 to Xcode 15. Migration should be straightforward and there is a step-by-step migration process that helps you migrate your code from one Xcode to another after you open your project with the new Xcode.
Additionally, I've found a post in the forums that may be helpful to you regarding localizable strings after migration: https://forums.developer.apple.com/forums/thread/738857.
To better understand the issue you're encountering, it would be helpful if you could provide the file structure before and after migration, as well as any errors or warnings that you encountered during the migration process. Additionally, it would be useful to see the differences in the .xcodeproj file, where all the changes made during migration will be displayed. If you have any other migration changes that you believe would be relevant to this issue, please feel free to share them as well.