After finding your matching doctoral program. You should check the eligibility, procedure and timeline of selected doctoral program. There is usually no one rule for the entire offered programs. It varies from course to course. Naturally, you can start applying from the most upcoming one till the time you get through to any one of them from your selected list of programs. Having knowledge of German is always an advantage but it is not must for each program. Refer to the eligibility criteria of the finalized doctoral program for German language proficiency level requirement as well.