*Missable*. In Gray Matter, a “dialog” is any text said by a character that gets noted down in either Sam’s notebook or Dr. Styles’ diary. So this can come from conversations with characters, or either playable character’s thoughts on items etc when examined. There, examine everything and anything possible in the game. Pressing select will display “hotpoints” i.e. objects that can be interacted with, examined, or locations to other places. Many objects will produce more than 1 dialogue either after immediately viewing or after something happens in relation to it or the story. Examine characters after talking to them, objects after use, objects in your inventory after collecting them, and look at everything when you’ve “zoomed in” on them.
It will take a while to get over 1000 dialogues, therefore it’s not a good idea to go for this achievement and Fast Play in the same playthrough. The time when the achievement will pop will differ depending on how much you examine etc. For me it popped during Chapter 6 as I was completing the second half of C Railer Swool, so by following the walkthrough posted above and this advice, you’ll get it either here or later in Chapter 7. Then feel good about not having to spend so much time looking at everything in the game, unless you like listening to Sam’s voice I guess.