Interesting idea, especially with an ‘authentic’ resource like that to potentially plug in. I can’t say his voice really bothers me in the first place, and each trilogy needs one film without subtitles! (And a crawl with no CAPS.)

Okay, those last two points are in jest.

What all aliens speak English in the films?

Nemoidians - sound like Asian accents
Gungans - fake dialect or accent
Watto - what I sound like trying to do either an Italian or NY Jewish voice because, while I like to have fun, I’m not an actor
Mas Amedda - British, speaking from behind makeup
Malastare senator - sounds like a female voice from the news
Yoda - odd voice and syntax
Ki Adi Mundi - British
Zam - sounds like a human lady while in human form, then with an audio filter while in normal form
Dex - fat guy from a sitcom
San Hill - oldish sounding voice
Techno Union guy - filtered
Grievous - filtered Eastern European voice
Utupau guy - odd voice
Unklar Plutt - slightly filtered British voice

I might have missed a few but it seems there’s plenty of precedent for this sort of thing so I’m not sure why it’s a problem, beyond some of your subjective impressions, which is fair enough.