Honestly, I think it's usually pretty cute when other peoples birds speak. I grew up with 3 parrots, none of whom ever spoke or even imitated a noise other than their own "parrot language" (which I actually find rather pretty and soothing). I'm completely accustomed to their noises and even the occasional screech fest. What I cannot tolerate are the birds who sit there and repeat the same word over and over and over again because they learnt it by the owner repeating it over and over again. As mentioned, Kiwi came with a small vocabulary, but he says those words in with his other normal noises (which is fine by me). He doesn't really seem to be a fast learner, and hasn't picked up any new words on his own in the 5 years we've had him. If he picks things up on his own (therefore doesn't repeat them like a broken record), that would be awesome, but I'm just not going to do anything to encourage it in case he picks up annoyingly repeating stuff.
I will add, I think at some point in his life, he must have lived near geese. If you've ever heard one of those big Canadian geese "honk", he sounds just like a big goose and I'm pretty sure that is not a natural parrot noise. I do encourage the honking noise because it's super cute, and if I honk at him, he'll honk back. He does the "whistle" game too. If I do the first half of the catcall whistle, he does the other half.