Do you need to read accented speech with an accent? Let’s think about it.
Dick Van Dyke is appearing in the new Mary Poppins film–not, blessedly, as Bert the Sweep, but in some other role. And according to Mr. Van Dyke, they had a dialogue coach glued to his elbow at all times. With reason. When the first Mary Poppins came out, people were a little more understanding about accents–or rather, it just didn’t seem to matter so much. But Van Dyke has taken… well, anywhere from teasing to abuse over the failures of his Cockney accent for fifty years.
Van Dyke is an absolutely wonderful performer (I’ve had a crush on him since I first saw him pitch forward over the hassock on the Dick Van Dyke Show), but he does not have a mimetic ear. Many actors don’t: far worse than Van Dyke’s Bert, in my book, was Leonardo DiCaprio playing Louis XIV and his twin in The Man in the Iron Mask, where Di Caprio, bless him, couldn’t pronounce his characters’ names. There’s no shame in not doing accents well–but you need to know that that’s the case.
So maybe, even if you hear the words you’ve written with a perfect what-ever-it-is accent, you’ll want to think carefully before giving voice to their accents. This is a time when enlisting the assistance of a friend can be useful. Read aloud to them and ask them to tell tell you if it works. If your listener says you’re more Bert than Sir Ben Kingsley, rethink.
But my dialogue is written in dialect! Okay, but you don’t have to read inflections that are not in the page. If you’ve got a character saying “I don’t know ‘ow!” you can soften the presumed “Oi” in I; if you aren’t good at the vowels, don’t hit ’em hard. And remember, it’s more important that your listeners follow the sense and meaning of the words than that they get a full theatrical performance.
You can also give the impression of an accent by varying your tempo, by changing your pitch, by adding a little vocal fry (vocal fry is when you lower your voice enough to get some gravel in it, which Wikipedia informs me is “produced through a loose glottal closure which will permit air to bubble through slowly with a popping or rattling sound of a very low frequency”). This last is a really good tool for a reader, as it gives your character voices a quality which can suggest age, gender, or social class.
Now, there may be a time when it’s important to the reading of your story that you be able to sound like Alfred P. Doolittle or Pepe LePew or Boris and Natasha–that is, that you sound like a comicstrip version of the accent you’re using. In which case, go for it.
What you want, in the end, is to read your words in such a way that the hearer is not distracted from the action, the characters, the story of your story. Even if you’re good with accents (or good with some accents…) don’t make that the focus of your reading. It’s just another tool.