I recently read her (retconned) origin story, and I think it's pretty easy to infer that as a child she did have an English accent. It seems plausible that it could've been dropped following her awakening from her coma, but she still refers to her mother (in reference or within that direct moment where she finds her - albeit - dead) as "mummy". This is more conjectural, but, she was also implied to have been staying within or near London during the entire point when she eluded both SHIELD and HYDRA. While not explicit at any point, exhibiting any accent other than an English one would probably pique more curiosity and draw her attention than otherwise, so again that would imply she would be at least able to properly pull off an English accent. However, in argument of her not having an accent though, she pulls off that disguise when she's with that guy who's working with HYDRA, which I would think would have her exhibiting some kind of low-brow American accent. I figured maybe if she's capable of pulling off all sorts of vocal inflections, she could've just chose to drop her accent when she permanently relocated to LA. Her voice actress also speaks with an American accent in MUA... In short - what's the deal with all of this?!

This is a bit off-topic, but it does tie-in with many of my points... Anyway, is the retcon considered more canonical in terms of her origin, or is the original one more widely accepted?

.... a hot one.

The Enigma says:

".... a hot one."

LMAO.

So why isn't that aspect of her character ever really noted in contrast to someone like Psylocke who's almost defined by her eccentricities of her ethnicity and heritage, or even Storm?

Furthermore, why is she portrayed as having an American accent in most other media?

It could be plausible that she dropped the accent, but I think it's more likely they didn't really care too much about what her accent is because you can't hear it and she was raised in a Marvel's fictional European country, although I'm not sure what kind of language they speak there.

or maybe its because she was raised by a cow in the mountains?