I never thought about this. Having grown up in near NYC and Balitmore shortly before The Wire it still seemed like there were things I missed. I can imagine even with subtitles there are some things that aren’t fully understood immediately just with word play.

But it's an interesting show anyway, even without the details.

I'd never really considered this. Grew up in the south-eastern US, with one side of the family from the Northern Neck of Virginia.

Accent was definitely Baltimore, but I never had an issue.

The Chesapeake Bay definitely has a lot of interesting accents on various sides, though: http://aschmann.net/AmEng/#SmallMapCanada

And I mean, they do have a scene where the cops have to hire a local lady who speaks the slang well to transcribe some of the conversations.

And yet Dominic West/Jimmy McNulty and Idris Elba/Stringer Bell are English and Aidan Gillen/Tommy Carcetti is Irish.

Idris Elba does an excellent job, but it’s a little easier for him since he’s given the most slang and dialect to use. Dominic West sounds American at least, but to people who know it, he doesn’t really capture the ‘Bawlmer’ accent. With respect to accent, Aidan Gillen is not great. It’s not quite “Littlefinger on the Chesapeake Bay”, but he never sounds comfortable in the accent. That it's easily overlooked is a credit to the overall greatness of the show.

Strangely, most of the significant characters in the drug trade are missing a Baltimore accent. I'm not really sure what accent Idris Elba is going for though it sounds vaguely New York City, while Method Man clearly sounds like a New Yorker when his character is from Baltimore. Wood Harris, who played Stringer's partner Avon Barksdale, sounds like he's from Chicago. The only ones speaking in a Baltimore accent are Proposition Joe, Slim Charles, and Snoop Pearson.

To be honest, his accent/affectation in Game of Thrones also always sounded kind of forced and uncomfortable to me. Still love his performance in both shows, though.