In ANH, Uncle Owen asks C3PO whether he speaks Bocce, 3PO replies "Of course I can, sir. It's like a second language for me." C3PO was created on Tatooine, Bocce may very well have been his second language.

Wookieepedia says that "Bocce was an interplanetary trade language comprising parts of multiple languages. It was created by the Baobab Merchant Fleet to allow communication between starcraft pilots, crews, and support personnel of various species. Though not commonly used by most, any experienced pilots or spacers would know a few Bocce phrases in case they came across those that did not speak the pilot's native language."When Anakin is talking to Padme in The Phantom Menace, he asks if she is an angel, because he "heard the deep space pilots" talking about angels. So, Anakin is hanging around pilots and the spaceport a lot, and is helping Watto in a junk shop which probably gets a lot of pilots and mechanics visiting.It's almost certain that Anakin taught C3PO Bocce as one of his first languages, so he could communicate with traders and other spacers. via /r/StarWars http://ift.tt/2AltQH7