I think that's what we should strive for. I know it's hard, but it can be done if we listen. Listen to foreigners and people from different parts of our own country, assuming you're from the U.S.A., such as Southerners, New Englanders, etc. Listen to how they talk, how they form their sentences. The word choices they use. For instance, only a Southerner would know how much a "mess" of beans is, or how far a spell is. And maybe I'm wrong, but I've only heard of a "frappe" (spelling is probably wrong) when talking to a person from New England. Or, how about a "hot ticket?" And what about those guys from the Bronx? How would you say, "Hey mister. You can park your car on thirty third and third street?" Would you be inclined to just read it as it's written, or would you almost instinctivelly add in the Bronx accent? (I'm not someone from another country would get this, but I'm hoping they will.)
So, you see, there are many things we can use, aside from laborious mis-spellings, to make a character "sound" like he/she is from some specific place. Try it. Listen to how other people speak, then try to copy it down on paper without using mis-spellings. It can work. I promise.