More people are functionally illiterate than you might expect if you're in a high IQ bubble like the tech industry. In 2017, 19% of American adults scored level 1 or below on the PIAAC literacy test: https://nces.ed.gov/fastfacts/display.asp?id=69
If the US has so many non-English speakers that it materially affects national literacy statistics, one might wonder how we ended up with an immigration policy that produces a permanent underclass of people who are locked out of meaningful jobs and are entirely outside the protection of the law, due to being in the country illegally.
Here's a sample reading test: https://www.oecd.org/skills/piaac/Literacy%20Sample%20Items.... It's a drawing of an ear, and the options are "ear", "egg", "lip" and "jar". You have to pick the correct word.