How to read/write International Phonetic Alphabet (IPA) characters from/to json file

Writing a JNI application in Eclipse on an Ubuntu machine. I will create a dictionary, essentially, out of 26 json files - one for each letter of the alphabet. The C++ side of the app will give me the option of writing new entries to the json files, or reading in already existing entries from them that will be used to construct C++ objects to be passed to the JavaFx user interface side for display. Most importantly, the phonetic spelling of each entry must also be included in the C++ object as it will determine what sound files are loaded and played on the JavaFx side. The only problem is, I'm not sure how to utilize extended character set in my code - specifically how to read and write the International Phonetic Alphabet from/to file.