I can't even get my hands on the works of Lem in English.
There is one version of Solaris published in English, translated by Joanna Kilmartin and Steve Cox 1970 which was not a translation of the Polish original but instead was translated from the French translation by Jean-Michel Jasiensko 1966. Apparently Stanislaw Lem was fluent in English and hated the Kilmartin and Cox translation believing it departed too significantly from his original Polish. How could it not be since it was a translation of a translation? He, however had originally sold all rights to the book and the Polish publisher who was responsible for granting translation rights apparently did not care that the Kilmartin and Cox version was poor. It sold well, and that is all they worried about.
Fortunately, while the Kilmartin and Cox version is still the only available print version, Audible.com earlier this year released an audio book version. Aware of the translation problems, and because it is in a non-print format they were able to negotiate rights to translate with the estate of Lem, bypassing the print publishers, and commissioned a new English translation which was done by Bill Johnston directly from Lem's original text. This new translation is widely regarded as superb and does an excellent job of bringing to life the story much as Lem intended. So while it is in audio download form rather than print, it is the recommended way to enjoy Solaris in English.