It’s a dead script that was not that common in the first place, in Kievan Rus’ it was even used as a form of encryption in XI—XVI centuries for how little spread it was. It is also very different from modern Cyrillic. So, saying “most Slavs don’t know how to read it” is a bit of an understatement. Noone knows how to read it, apart from some linguists and overzealous Witcher fans.
Kind of looks like the writing system of Georgian language but I’m not sure
No, this is Glagolitic script, an alternative to Cyrillic. Mostly used in old Slavic scriptures, was later replaced by Cyrillic and Latin.
Most Slavs themselves don’t know how to read this
It’s a dead script that was not that common in the first place, in Kievan Rus’ it was even used as a form of encryption in XI—XVI centuries for how little spread it was. It is also very different from modern Cyrillic. So, saying “most Slavs don’t know how to read it” is a bit of an understatement. Noone knows how to read it, apart from some linguists and overzealous Witcher fans.