How to install specific older version of Deluge with all the dependencies?

Original method for Ubuntu 19.10

You can simply install packages from disco on your eoan system with

cd ~/Downloads
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge-common_1.3.15-2_all.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge-gtk_1.3.15-2_all.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge_1.3.15-2_all.deb
sudo apt install ./deluge*.deb

and then lock their versions with single long command:

cat <<EOF | sudo tee /etc/apt/preferences.d/pin-deluge
Package: deluge
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: deluge-common
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: deluge-gtk
Pin: version 1.3.15-2
Pin-Priority: 1337
EOF

and enjoy:

$ deluge --version
deluge: 1.3.15
libtorrent: 1.1.13.0

Updated method for Ubuntu 20.04 LTS

You can simply install packages from bionic on your focal system with

mkdir -p ~/Downloads/deluge
cd ~/Downloads/deluge
wget http://archive.ubuntu.com/ubuntu/pool/universe/libt/libtorrent-rasterbar/python-libtorrent_1.1.5-1build1_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/libt/libtorrent-rasterbar/libtorrent-rasterbar9_1.1.5-1build1_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/main/b/boost1.65.1/libboost-system1.65.1_1.65.1+dfsg-0ubuntu5_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/b/boost1.65.1/libboost-python1.65.1_1.65.1+dfsg-0ubuntu5_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge-common_1.3.15-2_all.deb
wget http://security.ubuntu.com/ubuntu/pool/main/t/twisted/python-twisted-core_17.9.0-2ubuntu0.1_all.deb
wget http://security.ubuntu.com/ubuntu/pool/main/t/twisted/python-twisted-bin_17.9.0-2ubuntu0.1_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/main/i/incremental/python-incremental_16.10.1-3_all.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/p/pygtk/python-glade2_2.24.0-5.1ubuntu2_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/p/pygtk/python-gtk2_2.24.0-5.1ubuntu2_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/n/notify-python/python-notify_0.1.1-4_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge-common_1.3.15-2_all.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge-gtk_1.3.15-2_all.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge_1.3.15-2_all.deb

sudo apt install ./*.deb

and then lock their versions with single long command:

cat <<EOF | sudo tee /etc/apt/preferences.d/pin-deluge
Package: deluge
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: deluge-common
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: deluge-gtk
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: libtorrent-rasterbar9
Pin: version 1.1.5-1build1
Pin-Priority: 1337
EOF

and enjoy:

$ deluge --version
deluge: 1.3.15
libtorrent: 1.1.5.0

Thanks N0rbert! I have follow your instructions with a slight modification, all I installed was:

wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge-common_1.3.15-2_all.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge-gtk_1.3.15-2_all.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/d/deluge/deluge_1.3.15-2_all.deb

Then locked the update up with:

cat <<EOF | sudo tee /etc/apt/preferences.d/pin-deluge
Package: deluge
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: deluge-common
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: deluge-gtk
Pin: version 1.3.15-2
Pin-Priority: 1337

Package: libtorrent-rasterbar9
Pin: version 1.1.5-1build1
Pin-Priority: 1337
EOF

Followed by:

sudo apt-get install -f