SOLVED: The target setting "Use compiler to extract Swift strings" had somehow been set to No.
Aderstedt
Users receive reputation points by contributing quality content to the forums.
Posts include post and replies published on the forums.
Post authors can mark replies as Accepted to indicate successful solutions.
Apple Developer Forums admins can mark replies as Apple Recommended to indicate an approved solution
Last seen
User for
From
Sweden
Post
Replies
Boosts
Views
Activity
Additional information: I am able to completely break this in the same way in a new project by going into the intermediates folder and deleting the "stringsdata" files. They will reappear after a clean build, but the xcstrings file will show all strings as "Stale" in Xcode, and localized strings added in the code will not appear in the xcstrings file.