This is purely anecdotal, but so is everything else on this thread.
Where I used to work in Raleigh, North Carolina, we had a fairly heavy
immigrant Spanish speaking only population that we served. We had in
house 24/7 interpreters (as opposed to translators, there is a
difference I learned), and I asked one of them about the paperwork we
handed out that was in Spanish. Could they even read it? The consensus
was that most of them were illiterate in Spanish, which was eye
opening to me as we had a fair bit of money invested in software that
could spit things out for printing in either language....
Food for thought.

Ryan in Madison