NSLocalizedString only retrieves the key, not the value in Localizable.strings (IOS)
In my case it was because I had mistakenly named the file "Localization.strings" and hadn't noticed (it has to be named Localizable.strings). As explained previously the symptom is because the compiler cannot find the string. Otherwise the cause could be any number of things but usually it's a missing semi colon or quotation mark. These are hard to find when you're doing a lot of localizations at once. The lesson learned is to start building your localization file early on in your development process and build it as you go, so that they are easier to spot.
Same problem, solved using the filename: Localizable.strings
Change your .strings file name to Localizable.strings, it worked for me.