As far as i understand, at this moment GOG belongs to CDProjekt holding. A lot of older games available on GOG were in past times published in Poland by old CDP, i wonder if there is possibility to add a Polish versions of games to GOG offert? At least those which have this versions, most of them were really a piece of good work (CDP was the biggest Polish company involved in both translations and publishing). I was very happy when Black Isles productions from "Infinity Engine" series became available in polish version (in fact that was the moment when i decided to buy Baldur's Gate series and Planescape Torment), and would be very happy if other games (especially these having lot of text) would become available in Polish language versions.
Of course there is probably some problem with licences or something, but is there anything that CDP could not resolve? :D