Bucky just kind of laughs. For the limited vocabulary, the little guy does seem to understand what Bucky's saying.

"Not great, right? The more you drink, the less you can taste it." He takes a swig of the new bottle that Groot's handed him and then-- "Is it okay for you to be drinking? I've never met a tree that could talk before."

But he does have soot sprites living in his kitchen, so he's pretty open to whatever he meets as long as it isn't trying to kill him.