Voice

A writer is either going into a language or coming out of a language, a writer can only go one of these two ways.

I think that this is what they mean when they talk about 'voice.'

So what is meant by the word 'voice,' in regard to the writer?

That the writer either makes a virtue of language, or regards language as a vice.

The writers that speak to you are writers you identify almost immediately as speaking in a voice you can hear, in a voice that causes you to believe in the language they're using, whether they believe in it or not.