From my point of view, it is the Spanish cause most things has at least two to three names. Such as bedroom: pieza, cuarto, habitacion. Depending of the country in witch it is spoken. And it is still the same language and not a dialect.
Anyone that knows a tiny bit of Spanish will know that the vocabulary is so big that even for a person native speaker with a master can read literature in Spanish that will sound to him exactly as a foreign language. Try anyone to read Martin Fierro. You will need just a master in this book to read and undestand it. Spanish also took vocabulary from English, Arabic and many other languages. Of course for a English native speaker with even some education this fact can pass blind through treir eyes.