1) But for many people and in many situations, translation---including MT---is good enough. And that overcomes any perceived need to learn another language (which learning may be in opposition to learning something else, something perceived as more important).

2) Most people don't "consume" literature or poetry, and it's unclear to me that non-performance art requires language. (I appreciate Rennaissance painting, but apart from the occasional Latin writing I don't need language to understand it.)

Disclaimer: Besides English, I'm reasonably fluent in Spanish (more so 35 years ago when I last lived in a Spanish speaking country), and used to be reasonably fluent in German, French, Tzeltal and Shuar (and a bit of Italian and written classical Greek). So I have every reason to hope this study is correct. But I have my doubts.