Is there a feat or something that allows you to use your Int bonus for Diplomacy instead of Cha? I feel like I saw this somewhere, but I can't for the life of me remember where it may have been or what it was called.
There's a class feature from Inquisitors that allow you to add Wis to Diplomacy (and other Cha related stuff) in addition to Cha. I'm not sure if its that, and maybe you have mistaken it?
Perhaps you were thinking of the Rogue archetype: Kitsune Trickster?
Yup, it was Kitsune Trickster. Thanks VRMH.