Simplify the following text for a Grade 7 native English-speaking person.
Original: The libretto was adapted by Berg himself from Frank Wedekind 's plays Erdgeist ( Earth Spirit , 1895 ) and Die BÃ 1\/4 chse der Pandora ( Pandora 's Box , 1904 ) .
Simplified: Berg took the story from two plays called Erdgeist and Die BÃ 1\/4 chse des Pandora by the German playwright Frank Wedekind . Berg wrote the libretto ( the words for the opera ) himself .