I know this is a ttrpg community rather than a video game community, but I’d like to chime in and say this is something I really liked about Kingdom Come: Deliverance.

You start off illiterate, but there’s a quest to learn to read and afterwards, reading more books and such will improve your reading skills. Starting off, anything you read is literal gibberish, but then it becomes semi-coherent text with typos, and as you progress, it just gets clearer.

I could see this being something you could also incorporate in a ttrpg to add an extra challenge to your players.