It's a dramatic convention. They're 'speaking' goblin, and Rich isn't giving us words since we wouldn't understand them anyway, thus preserving suspension of disbelief when Goldie's talking 'common'.
Or something like that.
Wait, wait, wait. If everybody is suddenly going to start having and speaking racial tongues, it's going to violate 2200+ strips of continuity.
I know that all races having their own racial language (not to mention alignment languages and thieves' cant, etc.) is a big ol' D&D trope, but unless I've missed it, isn't everyone in the entire strip speaking and understanding the same common language? If underworld Drow and desert-dwelling hyena-people from half-way across the world are all mutually intelligible, then there's no reason to believe that this little band of goblins are all chatting in a Goblin language that even other goblins don't use.