Kubuntu 18.04 - running 32 bit program on 64 bit system

In order to run 32 bit program on a 64 bit system, some packages are required. For me, the following commands did the job:
  sudo dpkg --add-architecture i386
  sudo apt-get update
  sudo apt-get install libc6:i386 libncurses5:i386 libstdc++6:i386

  sudo apt-get install libgtk2.0-0:i386

  sudo apt-get install gnome-themes-extra gnome-themes-extra:i386

When installing a i386 package, if it announce you that it must remove some packages because they are no longer required, you should be careful: it might actually remove 64 bit packages and you will get a broken system.