So, for all GOG users who are missing the Polish dubbing:
1) go to your gog Galaxy app, click Installed games, right click on the Archolos game and select Manage installation ->Configure.
2) A windows opens where you chose language: Polish. An update is going to download (several GB, so wait).
3) When it is ready to play, go to your GOG Galaxy/Games/The Chronicles of Myrtana Archolos/Data and copy (make a backup) of the six KM_Speech1-6PL.mod files to your desktop.
4) In GOG galaxy app, click again Manage Installation -> Configure, select Language: English. (this time it will be very fast)
5) Move the six KM_Speech1-6PL.mod files from your desktop back to the Data folder.
6) Play the game with some epic slav voiceacting!
It would be good if the game would install the voices automatically, even when using the English version.