This is a list of packages which are considered important to be translated first if a team starts translating Ubuntu into a new language.
debian-install Ubuntu's installer. This package contains the strings of the text-interface-installer and the Ubiquity graphical installer. So these are the first strings someone will see when installing Ubuntu.
gfxboot-theme-ubuntu Contains the strings of the very first graphical menu of options during the installation process.
gdm The GNOME Display Manager. A login screen in the own language will make everybody happy.
gnome-panel Among lesser seen strings, this package contains the strings "Applications", "Places" and "System" which are seen in the top panel.
gnome-session Contains the "Shutdown, Hibernate, Logout, Switch User, Suspend, Reboot" and the description of the action related to each of those strings.
update-manager The update manager of Ubuntu