The source code of the application will be published over the next few weeks. Since then, all the developers will be able to contribute to the project by developing additional functionality to the application.

In the meantime, you can contribute by providing localisations for the application. Currently, we have people working on localising the app in these languages:
French
German
Lithuanian

If you wish to contribute, email us at dtg-android [at] cl.cam.ac.uk