2.1.  Checkout of the whole Debian Installer source tree

While translators can checkout only some subdirectories of the tree containing their translation files (done with subversion), developers need the whole source tree, which additionally requires the use of git and mr:

svn co svn+ssh://svn.debian.org/svn/d-i/trunk debian-installer
cd debian-installer
mr -p checkout

In the past, we had everything in one subversion repository. Then one day, the developer parts were migrated to git, while the translator files were left on subversion; this is why we have the project divided into two parts now.