Agrilla: I just did download a new version of BG2-EE-Clasical using and install it so see what wold happen.
For me it did work flawlessly and I can not see any kind of Galaxy-infection on my computer.
So I cold not recreate the error described by the OP. (hmm what is OP short for ? Ganni1987 thx for your answor)
I did the download using the GOG downloader (see
https://www.gog.com/downloader )
The files I got was
setup_baldurs_gate_ii_-_enhanced_edition_2.3.67.3_(a)_(10672).exe
setup_baldurs_gate_ii_-_enhanced_edition_2.3.67.3_(a)_(10672)-1.bin
So using the GOG downloader seems to be a useful way to get the "Clean" classic installers without Galaxy.
/regards.
edit
note the GOG downloader is GOG old download tool and is way older than Galaxy. And GOG it is not making any "comersial" for it any more.
edit Forgot to mention OS used. I did the install on windows 7.
I assume that the OP had Galaxy once installed on his system, perhaps a long time ago and that there are still remnants in the registry of his OS which triggered the galaxy related routines in the installer. It would not be the first time that somebody has problems installing a game after Galaxy is no longer on their system.
After a cleanup of the systems registry the installation should run fine.
Which nevertheless is concerning, is the circumstance that when you uninstall Galaxy (as long as uninstalling does not mean delete the folder manually) still remnants of it can interfere with the installation using an installer which is called "classic".