Updates
Gregg Press Witch World
I managed to obtain a Gregg Press edition of Witch World in very good condition, considering it's an ex-library book. It can be seen here, and in the Jack Gaughan section of Cover Artists, along with the full jacket art.
Lithuanian book
Today I received a Lithuanian translation of Witch World, entitled Raganų Pasaulis. It can be found in the Witch World collection, as well as under Luis Royo in the Cover Artists section.