StreamingAssetsUnity.cs

//ANDROID PLATFORM
string json = null;

string full_path = Application.streamingAssetsPath + "filename";

            // Android only use WWW to read file
            WWW reader = new WWW(full_path);
            //wait until the download is done
            while (!reader.isDone){}
            json = reader.text;
           
//STANDLONE PLATFORM

string json = null;
string full_path = Application.streamingAssetsPath + "filename";
            StreamReader reader = new StreamReader(full_path);
            json = reader.ReadToEnd().Trim();
            reader.Close();