The book-Aragorn, I think, spent basically his whole life preparing to be king. Why else did he spend times fighting for the kings of Gondor and Rohan - his future kingdom and future allies? Being a Ranger was his job - but it got him acquainted with the people and places of Arnor, and probably the lands between. He can speak Common, probably both forms of Elvish, and the language of the Rohirrim. He is friendly with most of the free peoples of Middle Earth.
The movie-Aragorn... well, if they're playing it that he never really wanted to be King, why can he do all these things? Is he just Middle-Earth's version of a renaissance man? However his character is sort of brought to more light and made easier to understand in the movie... I know people who consider book-Aragorn "a bit of a stick". Doubt you could say that about the movie version!