Smith's wife Emma once said that she believed God dictated the Book of Mormon because her husband could hardly speak clearly nor compose a clearly-written letter. The speeches and writings we have of him contradict this assessment.  In addition, others described Smith as articulate and descriptive from his youth on. Joseph”‘s mother, Lucy Mack Smith, wrote that when he was eighteen years old he used to amuse his family by describing:

“. . .the ancient inhabitants of this continent, their dress, mode of travelling, and the animals upon which they rode; their cities, their buildings, with every particular; their mode of warfare; and also their religious worship. This he would do with as much ease, seemingly, as if he had spent his whole life with them.”  

For more information, see The Mormon Mirage 3rd Edition:  A Former Member Looks at the Mormon Church Today (Zondervan, 2009). Also available as an audiobook and as an expanded-text E-book for Nook, Kindle and other reading devices.