Opera singers have to have powerful voices as well as a good technique. Most opera houses are very big, and the singers need to be heard at the back. They also need to be good at acting. They need to be able to learn their music quickly and to sing from memory. It is a help to be good at languages because operas are often in Italian, German, French, English or Russian etc. Some opera companies, like the English National Opera, sing their operas in English. Others, like the Royal Opera House, sing operas in whatever language they were composed in. Translations are printed on a screen above the front of the stage ("surtitles") so that the audience can understand what is being sung.