Per installare Mate su Debian Wheezy bisogna abilitare i repository backports:
# apt-get install lsb-release
# cat >/etc/apt/sources.list.d/backports.list <<EOF
deb https://ftp.it.debian.org/debian $(lsb_release -cs)-backports main contrib non-free
deb-src https://ftp.it.debian.org/debian $(lsb_release -cs)-backports main contrib non-free
EOF
# apt-get update
# apt-get -t wheezy-backports install mate-desktop-environment-extras
enjoy 😉