If I’m not mistaken, there is a difference between “Character voice” and “Accent”. Voice describes a person’ way of talking so that you’ll know which character is speaking. I think it could be considered something like how a person sound like in real life.
Accent, could also help in recognizing a character, but if there are more than one characters speaking in the same accent then it won’t be as easy.
When writing a character, I tend to keep an actor in my mind, or a specific role of theirs, which makes things a little bit easier.