Most of the Debian Documentation is available at http://www.debian.org/doc/ddp
Unfortunately, the DDP needs to be relaunched, there are not enough members in the project and few new members are joining the project. Meanwhile, other documentation projects such as Ubuntu (http://www.ubuntulinux.org/community/participate#documentation) or Gentoo (http://www.gentoo.org/doc/en/index.xml) are doing a better job at having new users join the project and develop new content and create translations.
Currently, there are several user manuals which are maintained, up-to-date and have a large number of translations including:
The Release document, available at http://www.debian.org/doc/user-manuals#relnotes
The Debian reference, available at http://www.debian.org/doc/user-manuals#quick-reference
Most developer manuals are not translated, but are up-to-date.
We still lack a sysadmin manual and an up-to-date user manual like most other distributions do.