Although communicating in English is no problem in many German research institutes, living in Germany is not just work, but also everyday life and recreation. An adequate knowledge of German makes it easier to integrate in daily life, particularly for families and it will make your stay in Germany more interesting. It is a very good idea to acquire a basic knowledge of German before you come and to develop some understanding of the written language and grammar.
If you or your accompanying family have little prior knowledge of German, several foundations will provide financial support for attending an intensive language course either before coming to Germany or during the first half of a scholarship. For example, the Alexander von Humboldt Foundation offers language scholarships of up to 4 months to attend intensive German courses at a Goethe Institute or another recognized language institute in Germany.
You can find an overview of organizations offering German courses, online learning methods, possible funding, and a list of all recognized German language tests in the Internet portal of the DAAD.
For further information on German courses, see "Language Courses at Bielefeld University".
If you are interested in a language tandem you can get more information at Teutoburger World Tandem.
Another possibility to learn German is to participate in integration courses. These courses are interesting especially for partners, as they take place intensively during a longer time period. More detailed information you will find here.