Additionally, if you're always being excluded from normal social circles, you end up only hanging out with people like yourself who also don't know how to read.

Additionally, if you're always being excluded from normal social circles, you end up only hanging out with people like yourself who also don't know how to read. So your group of misfits tries to cobble together their approximation of what reading looks like and ends up with their own misfit language. When they have to communicate with normal people again as adults, there's a disconnect.