“Library of Congress” is the “Tokyo Dome” of English journalism
Culturally bound size references are a bane of translators. For example, Japanese authors used to be very fond of giving land area references in terms of "Tokyo Domes." As in, "An area of forest equivalent to 112 Tokyo Domes is lost every year."
The English-speaking reader is liable to look at such a translation and think, What is a "Tokyo Dome?" How big is it, and why should I care?
I suppose that homely comparisons help our us wrap our poor monkey brains around really big numbers, but when you get down to it, even "Tokyo Dome" is meaningless as a measurement. If we can't grasp the actual size being talked about, then "112 Tokyo Domes" isn't much more use than saying, "It's, like, really, really big, OK?"
And while these kinds of comparisons might make for more interesting writing, they play havoc with translations. If you're writing to be translated, I advise looking out for and avoiding these kinds of references, or at least replacing them with something more neutral, like "soccer fields."
A similar phenomenon is happening in the world of English-language journalism, when talking about computer storage sizes. They used to talk about how many "songs" or "movies" a given storage medium would hold, but as sizes have gotten larger, journalists are talking about how many "Libraries of Congress" the medium will hold.
Like Tokyo Domes, who knows how big the Library of Congress is? All that a figure like "seven Libraries of Congress" tells you is that it's a whole lot of storage space. I think that giving a real number, like "100 terabytes," will at least help us compare to other figures; like, "That's 100 times the size of my hard drive." And it will make translation a lot easier.