To apply for a postgraduate degree in German as a foreign language in Germany, you must obtain a degree certificate of the corresponding major before you can apply.
However, it is difficult for German graduate students to apply for German as a foreign language, because the subjects of this science are different from those in China. Not only German history and politics, but also ancient German, the history of German development and so on, which are generally not learned in China.
Therefore, most students who apply for this major in Germany need to make up some credits from the fifth semester of undergraduate course, and then they need to write papers and defend with other students. After passing, there is basically no problem in going to graduate school.