The app was created using MIT's app inventor ( Feel free to look up its website). I created it after I saw a similar project posted on hackaday. The original poster used the raspberry PI - immediately I thought that a smartphone based app makes a lot more sense. The app uses google's text to speech functionality to change input messages into text. The text is then sent over the internet to Microsoft translate service for translation. The response is sent to the phone as an MP3 file which is played by the app.
Feel free to use and modify the source file. The project is functional, though it could use some polishing.