For openSUSE Tumbleweed run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/openSUSE_Tumbleweed/Education.repo
zypper refresh
zypper install goldendict
For SLE 12 Backports run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/SLE_12_Backports/Education.repo
zypper refresh
zypper install goldendict
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/15.5/Education.repo
zypper refresh
zypper install goldendict
For 15.4 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/Education/15.4/Education.repo
zypper refresh
zypper install goldendict