I'd recommend plutil on the command line.
plutil -convert xml1 in.json -o out.plist
It will blow up with NULL values in dictionaries and some other inconsistencies that iOS JSON deserialization will handle more gracefully, but it does appear to work pretty well.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…