StringsCheck is a command line tool and a Swift library for checking that strings files inside Xcode .lproj folders contain translations for the same strings.
Run StringsCheck from the command line by giving it path to a directory where you have .lproj directories, and a list of languages to check:
$ stringscheck /path/to/project/resources en fi svStringsCheck checks that each language has the same .strings files and each set of .strings files with the same name has the same messages in every language.