To get involved, contact maintainers Alexander Larsson, Christian Neumair, Dave Camp or Martin Wehner.
More information about getting involved with other GNOME apps (and many tips that apply to Nautilus) can be found at http://live.gnome.org/GettingInvolved
In most ways, Nautilus is a typical GNOME App; you should refer to here you can find more info on Nautilus internals
Just as many other GNOME applications, Nautilus is translated by the GNOME translation team.
All icons drawn for Nautilus should match the GNOME Icon Style Guide
If you want to write documentation for Nautilus, you should join the GNOME Documenation team.