Localizable.strings corrupted?
If this is your whole file, add a semicolon at the end. Change it to:
"Test locale" = "Test locale";
To get more detailed informations you can use the Property List utility from the command line:
plutil -lint <your_strings_file>.stringsthe -lint switch is for checking the syntax. If you have an error you'll get line number and more informations, and in general better directions on how to fix the issue.
You can verify your Localizable.strings file with this script: