Royal Academy of Dance was created in 1920.

Don't you mean,

"In what language was the systemised rules for Ballet written; for the Royal Academy of Dance in 1661?"

Depends what type. There is The Chester All Girls Royal Dance Academy

The Royal Academy of Dance was established in 1920 at the Trocadero Restaurant in Piccadilly, London by a small group of eminent dance professionals. Brought together by Philip Richardson, former editor of 'Dancing Times', the group included five European greats: Adeline Genée from Denmark, Tamara Karsavina of Russia, Italy's Lucia Cormani, France's Edouard Espinosa and Phyllis Bedells of England. They represented the principal dance training methods of the time. It was their concern for the poor quality and badly organised state of dance training in Britain at the time that led to the emergence of the Association of Operatic Dancing of Great Britain which eventually became known as The Royal academy of Dance and finally The Royal Academy of Dance

Dance Academy - 2010 Learning to Fly 1-1 is rated/received certificates of:

Australia:G