I tried testing in Polish with the Steam version (since switching languages in the GOG version requires downloading the full installer for that language) and didn't have any problem.

BTW since GOG didn't update to game version 1.506, here is an unofficial alternate download (1.8MB), containing the 4 files in the patch (div.exe, DivDialogSystem.dll, Osiris.dll, slash1.dll). The download is a self extracting 7-Zip archive (remane to .exe to run if you don't have an archive manager that supports the .7z format). Extract it into the Beyond Divinity folder, overwriting the files there (make a backup first, if you are so inclined), if required. The current version number is shown in the main menu.

If that doesn't help, did you try changing the game resolution, to see if that would make a difference?

If you are comfortable using a hex editor (such as XVI), you can replace 'Hero'/'Bohater' in the quickinfo.000 file in the saved game folder with a different character name, overwriting those characters and the ones following. In character creation there is a maximum of 22 characters that can be used, but when testing this in the English version, I was able to change up to 24 characters before causing any problems.
Make a copy of the quickinfo.000 file (or the entire saved game folder) first, just in case.