Sorry, I'm trying to remember the most influent writers.
Maybe Tolkien was not a great writer, but surely his influence on cinema, popular music, cartoons, etc... is on thing to consider. The same thing we can say about Edgard Allan Poe and Mark Twain.
In the other hand, we have the wonderfull Miguel de Cervantes! Don Quixote is enough to put Spain in the top of the list.
The same thing I could say about the Divine Comedy by italian genious, Dante Alighieri.
Antoine de Saint-Exupéry is a very influent figure until now, however there are a lot of better writers in the world, but they are not so influent as Exupery.
So, what is the criterion:
the quality of the work?
the global influence of the work?
There are rich books not very known and poor book very influents in the popular culture (things not always stay together)
And what about the Brazilian poets (Castro Alves, Carlos Drummond de Andrade, Vinicius de Moraes, João Cabral de Melo Neto, Manuel Bandeira) and novelists (Machado de Assis, Paulo Coelho, Monteiro Lobato, Jorge Amado)???
I hope someone know about them.
I know all the Brazilian writers are well known by the french people, the italians, russians... but I think the anglophonics don't know very much.