Here is a sample of cleanly-recorded conversational Simlish:
Robu la chobee; ahba ne snee. Tuvarro? Neva?
/ɹoʊbu lɑ 'tʃoʊbi: ˈɑbʌ ni sni: tu'vɑɹə 'nɛvɑ/

I believe it illustrates the American-accented-ness that posters here seem pretty well agreed about.

I am not sure why this is even up for question as the game is made in the US and the characters/voices done by American voice actors.

Also most of the towns are supposed to be in the US (or well, Simnation)

SV, TB, BP, SS, MF, AP, RW, LP, RH, propably MH, and propably also HS despite having its own royal family - continental US
IP - Puerto Rico
SLT - Hawaii
BB - jersey/guernsey
LL - moon of Sixam
AS - Iceland
MV - Tuscany
DV - Wales in an elven plane of existence

And if you include custom hoods, they’re mostly divided in:

Sunset valley clones
Riverwiew clones
Bridgeport clones
Sunset Valley/Riverwiew hybrids
Bridgeport/starlight shores hybrids
Mini sunset valleys
Mini riverwiews
Mini sunset valley/Riverwiew hybrids
Berry sweet Sunset Valleys
Berry sweet Riverwiews
Berry sweet sunset valley/riverwiew hybrids
Lunar Lakes but on another planet/moon

Making a completely different hood requires a lot of CC, store items, and CASt patterns.

What options do you have to accomplish that? Choose a voice of the three available? Set the pitch? That's all I can think of.

That is good enough for me. This is a game and they had thousands if not millions of things to program. I am glad we got the options we have.