You might not have an internal monologue. A lot of us don't, and the ones that do are equally shocked every time they find out. For what it's worth, I'm in the same boat—can form sentences, but why would I? It'd slow me down.
People who don't have inner monologues tend to assume that all that stuff is some form of analogy or metaphor. It's not. It's entirely literal.
Because I definitely dont "have an internal monologue about what I'm going to say" in the 100ms between when someone asks a casual question and I respond to it.
Yes, it is possible to maintain an internal monologue in real time conversation. That is one of the reasons why some people usually take longer than 100ms to respond.
People who don't have inner monologues tend to assume that all that stuff is some form of analogy or metaphor. It's not. It's entirely literal.