Where Did AppleJack & Applebloom Get Their Southern Accents?

[Ashen Pathfinder 16,151]

I'd guess that got it from their family. It's possible that both were quite impressionable at their young ages, and they just adopted the accent & lingo of the family as a whole; especially when they at get-togethers.

[Espurr 449]

......Wat?

 

You hear "US" accents all the time because you live in the US! The United States of America, right? Um.

 

Anyhow, Rarity has a Transatlantic accent.

Oh. That makes sense. Hm. Uh...

[babymoondust 223]

It also touches upon her accent in the mlp wikia. - 

 

http://mlp.wikia.com/wiki/Rarity

 

 

 

She speaks with a cultivated trans-Atlantic dialect

[Heliodor 156]

Rarity just wants to speak fancy-like. Her accent is a LIE!!

Okay, I legitimately laughed really hard at this...