The Department of German as a Second/Foreign Language of the Institute for German Language and Comparative Literature at Paderborn University offers free German language courses at all levels for international staff. You can join the courses at any time (apart from the A1 courses). Further information, a course schedule and contact details can be found here.
Writing Centre for international students, PhD students and researchers
The Department of German as a Second/Foreign Language also offers a Writing Centre („Schreibtreff“). In a variety of workshops you can for instance improve your proficiency in the technical jargon of your subject or your pronounciation. If you would like some support regarding formulating and revising your texts, you can get individual advice during the office hours.
In order to find a tandem partner with whom you can improve your language skills, you can also use the tandem market offered by the Centre of Language Studies.
Language learning websites
The Centre of Language Studies has created an overview of various websites with which you can improve your knowledge of German.