Hey all!
Instance in a recent game where a rogue tried to use diplomacy on a derro to de-escalate a situation. They did not speak a shared language, so it didn't work, but that lead to discussion on can a diplomacy check be made if you don't speak the same language.
For instance, if you're trying to de-escalate a situation, showing your hands don't hold any weapons, using a soothing/non-confrontational tone of voice, body language, etc - can you still "Make an Impression" if you don't have a shared language?
My instinct is yes, though at a higher difficulty, but I don't see why you wouldn't be able to? There's a feat for Intimidation that lets you use it non-verbally (Intimidating Glare) - but I don't see a similar one for Diplomacy.
There's a lot of instances in various media where characters don't necessarily speak a shared language, but they still manage to convey general meaning of a "we come in peace" type of way.
Definitely praying to the gaming gods that a Paizo staffer weighs in :)