I head canon most of the KNGs have british/english accents. This varies from just British to Scottish. (King since he's...a king, is British too of course.)
So I also think pirate has a more heavy, Scottish accent, probably like ones of old fishermen in the more secluded parts of Scotland or insular/Southern. Gruff and sharp, but they can still understand him. Burner, Dynamo, and Cold with more common British (Cockney more like.) Ground Man may have the same accent, but because he rarely speaks, it's unclear. Magic also has an accent, but can change it at will to a more "American" or regular. I Like to think Dynamo Man talks in a regular voice just because he got it re-modified, just out of self-consciousness. Excluding Tengu and Astro, since they both have canon voices.(Counting their Japanese voice tones).