Found this convenient summary table of the amount of books people had in their adolescence based on the PIAAC surveys.

Sikora, Joanna, M. D. R. Evans, and Jonathan Kelley. 2019. “Scholarly Culture: How Books in Adolescence Enhance Adult Literacy, Numeracy and Technology Skills in 31 Societies.” Social Science Research 77 (January): 1–15.

The Scandinavians are highest at around ~200 books; Anglos, Germanics, and Slavs tend to have ~150; strangely, Japanese and Koreans – only ~100 (Singapore especially is an outlier at just 52); the Meds around 80. Lowest is Turkey at just 27, joint second is Chile at 52; also the lowest IQ countries in this sample.

Heiner Rindermann in Cognitive Capitalism:

The number of books is the third best parental indicator of children’s intelligence (rBo = .25; Section 3.4.5) and at the international level the correlation is very high with cognitive ability (rBo = .70; Table 10.5) – much higher than any attribute of instruction or schools. The average number of books at home can be used as a proxy of national cognitive ability. Looking at the numbers taken from student assessment studies (see Appendix and Table A.3) the average for Latin America at home is 28 books, in Brazil 34 books, approximately a quarter to a third compared to Britain with 102 or Scandinavia with 111 books.

See also Steve Sailer’s commentary on (the paucity of) books in Mexico.

That said, I expect these correlations to start collapsing soon, if they haven’t already, as the most developed/higher IQ countries start shifting to e-books amongst the younger generations.