Simplify the following text for a Grade 6 native English-speaking person.
Original: Tristan und Isolde ( Tristan and Isolde , or Tristan and Isolda ) is an opera , or music drama , in three acts by Richard Wagner to a German libretto by the composer , based largely on the romance by Gottfried von StraÃ burg .
Simplified: Tristan und Isolde ( Tristan and Isolde ) is an opera in three acts by Richard Wagner .