The Qt4 library is obsolete, so it was removed from Ubuntu 20.04 LTS. Its manual installation is very difficult and long process.
So I would recommend to use schroot in this case.
We will install Ubuntu 18.04 LTS into it and follow my previous method.
We need to create and configure schroot first:
sudo apt-get install schroot debootstrap -y
cat <<EOF | sudo tee /etc/schroot/chroot.d/bionic.conf
[bionic]
description=Ubuntu 18.04 bionic
directory=/srv/chroot/bionic
root-users=$USER
type=directory
users=$USER
EOF
sudo mkdir -p /srv/chroot/bionic
sudo debootstrap bionic /srv/chroot/bionic
cat <<EOF | sudo tee /srv/chroot/bionic/etc/apt/sources.list
deb http://archive.ubuntu.com/ubuntu bionic main universe multiverse
deb http://security.ubuntu.com/ubuntu bionic-security main restricted universe multiverse
EOF
schroot -c bionic -u root apt-get update
schroot -c bionic -u root apt-get install git make pyqt4-dev-tools python-lxml \
python-whoosh libqt4-opengl python-gst-1.0 wget sudo \
libcanberra-gtk3-module libcanberra-gtk-module desktop-file-utils
cd ~/Downloads
wget http://archive.ubuntu.com/ubuntu/pool/universe/p/python-qt4/pyqt4-dev-tools_4.11.4+dfsg-1build4_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/p/python-qt4/python-qt4_4.11.4+dfsg-1build4_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/s/sip4/python-sip_4.17+dfsg-1build1_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/q/qtwebkit-source/libqtwebkit4_2.3.2-0ubuntu11_amd64.deb
wget http://security.ubuntu.com/ubuntu/pool/main/libp/libpng/libpng12-0_1.2.54-1ubuntu1.1_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/universe/p/python-qt4/python-qt4-phonon_4.11.4+dfsg-1build4_amd64.deb
schroot -c bionic -u root apt-get install ./*.deb
Then download source code of Ldoce:
schroot -c bionic -u root git clone https://github.com/ciscorn/ldoce5viewer.git /usr/local/ldoce5viewer
schroot -c bionic -u root -d /usr/local/ldoce5viewer/ make
schroot -c bionic -u root -d /usr/local/ldoce5viewer/ make install
To run LDOCE 5 Viewer use
schroot -c bionic -u $USER env DISPLAY=$DISPLAY ldoce5viewer
Optionally you can create desktop application shortcut with this command inside.