There is strong evidence that parrots can successfully imitate human language better than any other animal on the planet. Like humans, learn sounds by hearing and imitating.
Parrots are social creatures; they tend to try to fit in, in whatever environment they occupy. This explains why they copy human speech when they are introduced to a family.
Generally, birds are known to use language with other birds for finding food, nesting, and to avoid danger. Therefore, the parrot learns a human language to communicate so that it gets noticed and its needs are met.
Parrots learn a language faster when humans communicate to it often. The more you use a particular word when interacting with the bird, the more comfortable they will become with using that word. Praise also works wonders. It encourages them to talk more hence improving their language.
Some parrots with the most advanced language abilities are; Electus parrots, Timneh African grey parrots, and yellow-naped Amazon parrots.