Generally, German is the language of instruction in most of the degree programs at German universities. Foreign applicants are usually required to prove their knowledge of the German language before getting admission.
However, German is not a pre-requisite when seeking enrolment in an international degree program or a special post-graduate degree.
Knowing German is not a requirement for studying in Germany. Many universities offer English-language postgraduate programs. It will also be determined by the course for which you wish to apply.
Ideally, it is best to enquire directly with the educational institution in Germany as to their precise language requirements.
However, studying for free in Germany means that there would be no or very low tuition fees. This is so at public colleges, where there are no tuition fees. Fluency in German or an average of 80 percent for certain universities are among the requirements for admission.