Sketch, can't talk. He can make random sounds, like all Skrawings. He is stubborn, confusing but at the same time, helpful. In Game Freak 2, you get a "Skrawing Translator", which translates all of the random sounds made by Sketch, and his species (although unseen), into English (or whatever language you're playing the game in).
“Hi everybody! I am Sketch, one of the most courageous Skrawings. I have come from my lovely town of Sketchville, in order of the king to help you defeat this... BOX fellow? Oh HAX! Sorry!”