If were talking pretty in an aural sense, I think you'd be hard pressed to surpass the flowing beauty of the languages of the Native American nations of the upper Midwest. The Sauk, Fox, Chippewa and Ojibwe nations really ought to get more props for creating the most beautiful languages ever. Words like Minihaha meaning 'laughing water,' the name of a waterfall, or Oskaloosa, meaning "the last beautiful one" the name of a Native American princess. Its a language of o lot of pleasant vowel tones with a lot of double consent sounds, like Mississippi.
Heck, even the tribal names Chippewa and Ojibwe are pretty words.
