Puppet isn't so much of a language as it is an incantation phrase book powered by souls devoured thousands of years ago and given form by the heartache of opsen everywhere.
Madness string 82887
Most of his disciples were common laborers and likely would have had little to no formal education. So who exactly would have taught them to read and write? I think people can't grasp the fact that throughout history most people were illiterate, and that simply because much of the world has decent literacy rates that the same situation existed in the past.