GRE

Yes learning german is helpful as you need to interact outside the course too. Since you hvnt mentioned the course you are interested in, here is the list of requirements.The eligibility criteria may differ from university to university. So please refer to the University website for the eligibility criteria for the course that interests you.
1. Academics
Certification of Undergraduate study (Bachelor degree) in similar field
2. Language Requirement
If the course is completely in German, then proof of proficiency in German Language
German as a Foreign Language Test (TestDaF)
German Language Test for the Admission of Foreign study applicants (DSH)
If the course is in English, then proof of proficiency in English TOEFL (550 and higher (PBT), 213 and higher (CBT), 79 and higher (IBT) ) or IELTS 6.0
For bilingual courses, appropriate proof may be required
3. Entrance qualification
For engineering courses, some universities may demand GRE
For Business management courses, some universities may demand GMAT
Some universities require the student to take entrance test either online or upon arrival at the campus (in the later case conditional admission is provided)
4. Work Experience
Improved chances of admission if relevant work experience in the field of further study
5. Project Work / Thesis
Demonstration of technical ability through project execution
6. Extracurricular activities
Paper presentation, participation in Technical symposium, conference etc will be highly appreciated.