R'lyehan is a difficult language. It has conjugations and declensions that are literally incomprehensible to mortal minds, and that's not even getting into the tense-aspect system.
So you really don't have to make many errors in your chanting before, instead of summoning the Crawling Chaos, Messenger of the Outer Gods, the Black Pharaoh, He Who Watches From The Darkness, you wind up summoning a very confused ex-Asmodean cleric from several solar systems away.