It is necessary to have a basic or intermediate level in the language of your host country in order to have a successful au pair year abroad. Before your trip you should take some time to practice the foreign language. You can read easy books, watch movies or take a language course in your home country. The more secure you feel in the foreign language before your trip, the easier it will be for you to adapt to being an au pair in your new host family.
You can practice your listening comprehension by playing DVDs in the language of your host country instead of watching them in your native language.
You can also prepare for your au pair stay by watching talk shows or live shows in the foreign language. In these shows, people speak naturally, without a script. There are only a few movies which are as difficult to understand as the spontaneous conversations of a talk show. Talk shows are also great because people use a lot of slang.
If you like movies, you can rent ten of your favorite movies and watch them in the foreign language.