You are taking about the Kinderhook Plates.
No documentation ever states that he tried to translate them, that is credible anyways. There is documentation that he requested they be sent to scholars for authentication before he would spend time with them.
You gotta remember, back then, people were calling BS on him all the time, so just because a 3rd party document from 175 years ago says he tried to "translate" them and was fooled, could be an outright lie. Haters lied about him in court just to get him arrested, only to be released later the same day because of false allegations.
Since there is conflicting stories regarding what actually did happen, (Some claimed he was fooled, some say he didn't want anything to do with them until they were authenticated), you can't really say what really happened because it's a he said/she said type of bs.