In your situation, two ways to acquire residency look promising. First is the EU blue care (for high-paid/desired professionals who are sponsored/contracted by a company in Germany). Second is a GmbH-setup residence permit (you invest and set up your own business, GmbH, in Germany).
How can I apply for a German resident permit for the purpose of self-employment as a freelancer?
I am a Chinese-German interpreter with years of professional experience. I travel frequently between China and Germany and have worked for several prestigious German companies. I was informed that freelance professionals might be able to apply for a German resident permit. But due to the nature of the work, it is hard for me to provide a business plan. Is my background strong enough for the application? Do I need any kind of sponsorship or contract from a German company as evidence of a commitment to living here?