There is an app in the Apple App Store that downloads custom dictionaries and programmatically adds them to the iOS's built-in Dictionary.app without user intervention. It works normally with the stock ROM, i.e. no jailbreak or anything of that sort is required.
I wonder how this is possible since Apple has never documented such a "feature." There is no API or hints in the iOS and Dictionary.app documents to explain how this is done.
How could this be implemented?
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Link to original article：https://stackoverflow.com/questions/23019109/programmatically-expanding-ios-dictionary-app-lexicons