Part of the writer's intent is reflected in the way the NPC responds.
Also, this isn't like the real world. The writers know what the PC's line is and can craft their NPC's response accordingly. That doesn't happen in real life, which is what leads to confusion between the intent of the speaker ("Sorry, I didn't mean it that way!"), and the reaction of the listener ("But that's how it sounded.")
This would require some useful mechanism for predicting the NPC reaction. And I don't think we should have one.
The writer's intent is only in the game if you decide it is.
So let's assume it doesn't happen in the game either. That neatly solves the problem.
Let's talk intent shall we? I am an actor, and thus, I spend an inordinate amount of time figuring out the intent of a character and how to reflect that when speaking. Because, and don't get this wrong, EVERYONE has intent. Intent is why. Why are you saying this. This can manifest itself into wanting something from someone, maybe a reaction, maybe a physical thing. Other times it's because it *needs* to be said. Such as 'character's mother just died, thus he is world-raging', this is also wanting something. Someone to tell you it's okay, or that *mother-dying* didn't actually happen, or simply for release.
In the realm of silent VA for a main character, and VA for everyone else, intent manifests itself as everyone else's lines. Because, 8/10 times, intent WORKS. It does. If I wanted to ****** you off, I could be sarcastic, accuse you of something, laugh *at* you with acid in my tone. Calling Alistair a royal bastard means he responds positively, treating it as a joke, because that's what he heard. You (the player) don't have control over intent. It's just the writer's intent instead of the characters. if you (the character), said that line sarcastically, or with derision, in order to get a negative reaction, said negative reaction would have happened. Alistair wouldn't have laughed, or took it well, he would have, again, responded in kind, upset or angry. Because, behind Alistair is an actor (yes, an actor), and he's responding to the line in addition to it's tone or intent. He's being told (most likely), what the PC is saying is a joke. And he responds, in character, to *that*. If he was told, it is being said with a blank stare, his reaction would be entirely different. If he was told to react to every scenario, all of *his* tone would be lost and the acting would suffer. Because there is no proper response to everything a line could be. Too many contradictions to make anything other than an exposition dump plausible. People react to how a person says something more than what they say. EDIT: There are catch-all responses, but they also tend to lack intent and translate into non-emotional "...ok....". Which says nothing about anything really.
Short acting lesson:
When getting something from a conversation, a reaction to how one is behaving, what their inordinate goals are, etc.
~60% is body language.
~30% is tone, i.e. how a character says something.
~10% is what they are saying, and this number often goes down depending on what one is saying (the others go up.)