Linguistically speaking, Norwegian is the easiest language for an English speaker to learn. Most assume it would either be Dutch or German, but this is false because verb conjugation is easier in Norwegian (it's even more simple than the other two major Scandinavian languages: Swedish and Danish)
As far as literature, I'm completely ignorant of anything of note produced by Norwegian authors, so I can't help you there.
French used to be lingua franca of not only Europe, but most of the planet, for a good few hundred years. It was the language of science, international affairs, diplomacy, and was the main medium of instruction in most schools outside of Europe (For example, in the Ottoman Empire, you'd hear more French being spoken in the street than Turkish as all the minorities, as well as the native Ottomans, used French as their lingua franca).
This was true until relatively recently, after the end of the second World War when the United States became a superpower and English was given the prestige status. To give you an idea of how quickly the planet shifted from French to English, in 1948, most European diplomatic corps were entirely Francophone, but by 1950, they were replaced by Anglophones.
French literature is rich and massive in scope, I can't even begin to do it justice here and there are many works that were only translated to French (remember, French was the global lingua franca, if you wanted your work to be read by the rest of the world, you only needed to translate it to French), so there's a trove of works that have never and will never be translated to English that you can read if you become literate in French.
For ease and for the novelty of being fluent in a European language, Norwegian would be the easiest route to go, as for actual usefulness (French is spoken in forty countries, Norwegian is only spoken in Norway) and literature, French would hands-down be the best option.
t. Linguist