Unless the literal words are important to moving your game forward, you should summarize the majority of NPC dialogue.
I've been recently dealing with this issue in my games, where the in-game word choices (of NPCs, journals, and such) were interfering with the gameplay. Every NPC has their own accent, opinions, and hidden intents, and when the players wanted to interact with them, we would play out the entire conversation, word for word.
Unfortunately, the problem with this strategy is the DM's verbal skills become a bottleneck on their ability to narrate the world to their players.
First of all, it's exhausting trying to improvise a full conversation while tracking different NPC voices and perspectives. This is especially true when multiple NPCs are involved.
Second, when you the DM are picking all the words that your NPCs say, that means the player characters are socially interacting with you (the DM) and not your NPCs. Whether the NPC is an expert liar, or an experienced diplomat, or simply an intimidating brute, their dialogue will be limited to your own vocabulary, slang, and other verbal habits if you focus on word choice.
Third, and here's the kicker, we as DMs tend to overestimate our ability to communicate the world to our players. By focusing on word choice, rather than emphasizing the intent of the dialogue, we're giving the players a lot of unnecessary detail. And that can confuse your players, and distract them from the speaker's intent. Why did the NPC use this word instead of that one? Why did they say it this way? Or maybe you chose the NPC's words because they are implying something, and none of your players picked it up.
The game will become smoother for both you and your players once you focus on the intent of the words and less on the form. Summarize. Get to the point. Most of the time, the formal word choice doesn't matter, and only serves as an obstacle to narration. Don't read out what your NPC says; tell the players what the NPC means to say, and let them figure it out.
If you still want to roleplay as the NPCs, then there is a convenient hybrid approach. Roleplay the first few lines of speech, such as greetings and openers, and then, as the DM, you summarize what the NPC says. Then let the player characters respond. Maybe speak as the NPC a few more times during the conversation. This solution is handy because you get both benefits: you establish the flavor of the NPC by briefly speaking as them, and then you return to the narrator role and have more freedom in communicating to the players.