Quelle phrase preferez-vous pour dire "Let's go"?
Literally, the "y" means "there".1) Is the "y" on allons-y purely colloquial, like the "y" in "il y avoir"? If not, what does it refer to in its pronom role?
I definitely agree with LV4-26 : Allons-y isn't colloquial at all.I wouldn't say allons-y is really colloquial. It's rather standard.
3) What is most appropriate to say to my cat as "encouragement" when we're walking to her food for dinner? I've generally said "Allons-y!," but Agnès mentioned above it may be somewhat formal.