Charlatan
 

In English this means conman or faker or imposter. I noticed that Spanish dictionaries state that charlatán may mean non-stop talker, fast talker, and charlatan. Is charlatán commonly used to mean imposter or is its meaning ambiguous?

Oh, I didn't know this.
I've only heard "charlatán" used as you define the word in English, Poli.
But I just asked someone older than me, and they are quite comfortable with the word referring to a person that will speak non-stop or that talks nonsense. The use might be a little archaic. :D
I'm not really surprised though about this meaning; it has the root "charlar" (to chat or to talk nonsensically) in it. In context, I wouldn't have objected the use. :)

I checked English dictionaries to see if charlatan has any alternate meanings, and it doesn't, but the term fast talker has negative connotations related to the term charlatan.

Thank you Angelica for confirming what I suspected.