Librarians go to school to learn how to manage information, whether it is in book format or otherwise. (We tend to think of libraries as places with books because, for so much of human history, that's how information was stored.)
They are not supposed to have more information in their heads, they are supposed to know how to find (source) information, catalogue and categorize it, identify good information from bad information, good information sources from bad ones, and teach others how to do so as well.
Duolingo got me enough vocabulary in Spanish to put the simplest sentences together, and then follow more robust lessons. I still think it was a good starting point, but I won't use it anymore on principle.