I recall reading a TwiLuna fic some time ago that had a chapter where Luna meets Octavia and Vinyl Scratch in Ponyville. Vinyl Scratch is a mute in this fic and communicates via sign language and Octavia translating. One part that's stuck in my head is where she makes a sign and Octavia says "No, I will not say 'What's up, home skillet'!" or something similar.

There's also a part where Luna is confused when Vinyl is referred to as "mute" and then it's revealed that the condition was referred to as "dumb" in her time.

Thanks in advance if anyone can help me find this fic.

One of my favorite TwiLuna stories. 'Twilight, Good Night'.

Twilight, Good Night is a fantastic story and yes 100% the one you are after. It is well wroth the read for anyone who hasn't its a very adorable TUNA fic and also one of my favs

it's this one, I think:
https://www.fimfiction.net/story/247622/twilight-good-night

I was just going to say the same thing. Twilight, Good Night is one of my favorites.

Thank you for asking this question, I hadn't read it before and am now half way through it.