Tim Sheppard in his guide to storytelling makes the following suggestions on using accent and voices in your stories:
“There is a wide consensus that it’s okay to tell stories from another culture, with the proviso that you ‘make it your own’ – as with any story. If you normally use character voices successfully in your stories, you may want to use foreign accents in a foreign story. This is highly dubious. Making the story your own includes telling it from your own perspective, with your own voice. If you have grown up partly in that foreign country, that foreign accent may well be an authentic part of you – fine, then you will also know any cultural sensitivities to beware of. If not, any attempt at the accent will probably come across as a caricature, especially to native speakers. People can get very offended by caricatures, but they don’t get offended at heartfelt attempts (even when inept) to communicate genuinely – so stick to what is part of you. You can be welcomed telling a very foreign story to its own natives if you are heartfelt and respectful.”
That said, different “voices” for different characters can be highly effective in enriching your stories. The use of vocal modulation can aid in this. Such techniques as using short choppy phrases with a higher pitch can denote a child. A raspy, shaky presentation can be used to denote age. Be sure to practice ant of these in advance so that you do not lapse into your neutral (narrators) voice, or worse still confuse your characters’ voices.
So, stick to an authentic voice. Use only accents you are sure of. Try to avoid stereotypes. And once again find your own voice.