An au pair needs basic knowledge of the language spoken in the host country. If the au pair does not have the necessary language skills, he/she will most probably not get a work permit (which is required in many countries).
The au pair should at a minimum, be able to answer simple questions and make himself/herself understood in a simple way.
Please note: Even if you, as the host family speak the au pair's language or you are able to communicate with the au pair in a third language, this will not be sufficient. The au pair looks after children. If during your absence an accident occurs, the au pair should be able to call for help. You cannot assume that people on an emergency services telephone line can speak or understand the native language of the au pair.
You can do even more for your personal safety. The following page will provide you with more information on safety aspects.