How do you know từ điển is plural? Couldn't there be one famous dictionary?
If they give me the name of the library, I could check.
I will be curious to know which libray they are talking about ;-)
According to a french magazine, the 10 most beautiful libraries in the world
Presumably, we use 'một' to indicate 'one'. Still confusing that there's no classifier (e.g. cuốn/quyển) used to indicate that the dictionary is a type of book.