This is not really a big deal. Some writing systems require you to recognize a few thousand symbols, and I read (i.e. "effortlessly recognise") three alphabets and with some concentration two more (the grammar is a bigger deal for the latter...my overall fluency in those languages is, at best, poor and I am sure will never get better. But symbol recognition is not the barrier).
This is because I put in the effort to study these languages, but many people, without much formal education, can read that number of alphabets (much better than I can) simply because they live in (typically border) regions where that is reality of daily life. My own mother grew up in a town where four writing systems were in use, plus used a different alphabet in her home.
Don't mock that older writing by the way. Most people were illiterate; Especially anything in paper was the writing of some pretty sophisticated folks.
Only about half the glyphs to recognize. Being able to skip further down the "page" and trivially continue reading. Being able to rapidly scan a line of text.
I guess this is all predicated on a mostly literate populace with a lot of reading material. You probably don't need to rapidly scan a wall carving extolling the virtues of your God-Emperor and recording all of his battle victories, unless you're trying to win a bar-bet. ("I'm telling you, he beheaded TWELVE infidels with a single swing!" "Yeah, well, find it on the wall and I'll buy you a beer.")