Given the current situation (basic education is widely available) literacy in this country should not be a problem. If you cannot read, how could you fill out a ballot in the first place? What scares me with illiterate voters is the following scenario:

An illiterate voter goes to the polling place, given a free ride to the polling place by (fill in the blank, your favorite or least favorite special interest). The person asks the volunteer transporting him or her " I can't read and I want to vote for ------, which place is he/she on the ballot?" The voter is told, but is told the position of the candidate who the group supports. The voter believes he/she has voted for their candidate, but has actually voted for someone else. BTW, this has happened in the past, yet another reason that registering to vote in the auto registry office (aka "motor voter" bills) scares the bejesus out of me. I don't know who decides, but there has to be a minimum standard of competency at some point.