To receive a residence permit you need to prove that you are, to some degree, in control of the German language. In order to do so, you will want to pass an exam, the GOETHE-ZERTIFIKAT. B1 is what you need if you are aiming for the Niederlassungserlaubnis.
In 2019 we held our first and therefore guaranteed best WordCamp in Düsseldorf. It was a complete success and lots of fun for all participants.