1pod
There is the "standard" way Apple of localizing iOS apps using NSLocalizedString. It's versatile enought and you should stick to it unless you have good reasons not to.
I reuse the same localization files in an iOS app, on a web site and, possibly, in an app made for another platform. Advantage of JSON there is that libraries for handling JSON are available for just about any modern platform.
As a side advantage, it is much easier to create tools which do not rely on localizers being proficient with escaping C strings or use translation services not geared towards iOS app localization.
License: MIT