Here's the original story from 404 Media that this tweet is paraphrasing (without linking to, of course, because X disincentivizes links): https://www.404media.co/ai-companies-are-buying-tons-of-old-...

The segment that talks about rare books:

> One professional bookseller who specializes in selling foreign language books on these marketplaces told me that, starting in April, he and other booksellers noticed a historic spike in sales. [...]

> This bookseller said his inventory is full of rare, foreign language, and low circulation books, meaning that if they are destroyed in the process of becoming training data, they’ll be even harder to obtain.