This command line program detects unused resource strings in an iOS or OS X application.
Updated to Swift 3, thanks to @astaeck on Oct-17-2016
Open a Terminal to the directory which contains the AbandonedStrings executable, and run the following command:
$ ./AbandonedStrings /Users/your-username/path/to/source/code
If a .strings file contains…
"some_string_identifier" = "Some Display Text";
…this program will consider that resource string to be abandoned if…
"some_string_identifier"
…is not found in any of the source code files (namely, files with a .h, .m, .swift or .jsbundle extension).
This program searches through the source code files in an iOS app project, looking for resource strings (in a .strings file) whose identifiers are not referenced by the application's source code.
The search logic does not take into account if code is commented out, so it won't be as reliable if your application has a lot of commented-out code.
It also does not try to determine the context in which string identifiers are used, such as whether or not the string is being used to look up a localized string value or if it just happens to match a resource string identifier by coincidence.
Also, this program is ineffective if resource string identifiers are referenced via constants or dynamically constructed.
As noted above, this program uses a simple heuristic and is not guaranteed to produce perfect results for every codebase.