Reading is a separate skill from speaking. I’m certain those illiterate people have no problem communicating verbally.

Most of Europe speaks at least two, and most of Switzerland 3. I think this might be an effect of the American education system.

Learning language is not that impressive as a cognitive/educational feat. It is mostly a simple matter of practice. School reform is not going to change this. Case in point, Canada where schools are good and French is mandatory struggles to actually teach anyone how to speak French. For Europeans the standard second language is English which is pretty straightforward as a result of globalization. Adding a third language that is spoke by everyone an hour train ride away is not that much extra.

Europe and United States have nearly equal land area of just shy of 4 million square miles. There are 24 official languages of the European Union and English as the lone, defacto language of the USA.

Why would anything else be expected from the American education system when, for example, you can travel the entirety of the US and most of Canada and not have to worry about finding someone who speaks English. The education system in the US is trash for a few reasons, but only teaching English to all is not one of them, and I say this as someone who lives in the US and speaks a few languages.

I’d have to imagine a good portion of that is most likely from immigration though.

Even if you’re a native English speaker if your parents are 1st generation Americans there’s still an effect on educational attainment especially depending on the cultural background. It’s a chicken or egg situation. Whenever aggregates are brought up about the US educational system it’s questionable. This country is so large and diverse. I believe if you cut out the Deep South and poor inner city communities our educational rankings shoot back up to the top. There’s a reason the best universities in the world are still in America. It’s not like public education is neglected until college age we just have certain parts of the country that drastically underperform and it’s lot easier to have those parts when it isn’t a small homogeneous community.