Putting that into their "find a book", and telling it the kind of books I'm looking for, I get a bunch of book recommendations. They are English language books, but I know where I can get hold of some of them in Russian translation. I can see, for instance, that Jasper Fforde's fantasy books are rated as being about as hard (maybe a tiny bit harder) than the Lord of the Rings books, whereas the last 3 Harry Potter books are rated as being quite a bit harder. So that's my next 3 or 4 books sorted out, with a minimum of of reading, checking and worrying on my part.
This does assume that the Russian translations stay faithful to the originals in terms of lexical complexity. I've seen some translations where the original text has been considerably simplified for a younger audience.
With Japanese the system is less helpful for me, because my reading skill is kindergarten level. At this point the "find a book" tool recommends kindergarten reading schemes which are probably not available in Japanese translation.
What I would like to do is to be able to say to one of my students: "What's the last book in English that you read and enjoyed?" and from their answer be able to work out their reading level and give suggestions for their next few books.
Another point is that the system is designed for young American readers. Children's books and young adult books are favoured, which can get boring for an older reader.