Ghostwriter is from way in the past, and there's a lot of Wild Mass Guessing with hints of Word of God that says he's an escaped slave. So how come he speaks in such obviously 1990s English and not 1850s English?
With his set of skills, it's quite natural that he would very quickly be able to pick up new lingo and styles just from doing a ton of quick reading and absorbing of language patterns.
It helps that Ghostwriter asks about the meaning of words or who people he doesn't know, such as who is Mickey Mouse in "To Catch a Creep".
In the "Lost in Brooklyn" episode, why didn't the girl simply call a taxi and ask her dad to pay?
Well, it's easy to assume that since she was from Mozambique that she never used a taxi before and her dad forbid her from entering strange cars. That and she was 13-15, they're not always going to think rationally.
The later part of the show's run is often criticized for letting so many characters see Ghostwriter. However maybe that is because he was nervous about revealing himself to too many people at the beginning. After positive experiences, he becomes more comfortable with letting more people see him.
In one episode, Ghostwriter reveals that he's afraid of dogs. Might not mean much...until his backstory as a runaway slave is revealed. If he was in fact a runaway slave being hunted by the authorities, and if those authorities had dogs with them (which they probably did, as is common for any age), and if those dogs had something to do with his death...
Oh, and there's more: One of Ghostwriter's first lines is frantically asking if "the children" are all right. If he really was an escaped slave killed while with any other escaped slaves, and if any of those slaves were children...oh, God...
