Anyone who speaks as I do has no accent. It's all the rest of you guys that give me trouble!
Seriously, though, I agree with TubeTote. You do tend to adopt the speech patterns, including both accents and vocabulary, of the area in which you live without realizing it. I also have found that my ability to understand depends on extent of exposure. Years ago in graduate school research labs I worked with people from England, Ireland, India, Australia, China, Japan, Pakistan and Kenya. They didn't have to be in the lab very long before I got used to their accents and was able to understand almost everything they said. But my first meeting with, say, someone with a Russian accent would not go well. We learn through exposure and listening.
Local dialect can become intimately entwined with all life aspects, including cultural norms. I had a manager who told an interesting story. He grew up in Newfoundland. There, he says, it is or was normal to refer to any man as "boy", with the exception that certain people, especially older ones, who deserve extra respect are addressed as "Capt'n". In other parts of the country we might use terms like "guy", "buddy" "sir", etc. Later in life he managed a large factory in Alabama, where he realized VERY quickly that nobody addresses anybody as "boy" unless you want to risk a major dispute with racial overtones.