Rokket is onto a good thing here. I've found that the more I do silly impressions and accents, the better I become at them; like anything else, practice! I guess it doesn't help any if you're no good at adapting your voice like that, and not everyone is, or has the time to practise. Aside from manipulating your own voice yourself (doing impressions) or using voice actors/actresses, I'd think you would struggle. There are good packages out there for voice changing, but they're largely all the same (from what I've seen) and don't give all that great of a result, especially for quite drastic changes.

I'm running Win 10 Pro 32GB RAM Intel Core i7-4790K CPU @ 4.00GHz Nvidia GeForce GTX 1660 Ti

My DA Gallery: glen85.deviantart.com/gallery

Peace, love and polygons!