As someone who learnt to love German in her twenties and lived and studied in Germany for many years, I can provide you with methods of grasping the essence of the language quickly, and of mastering it steadily, many of which are not obvious to the native speakers.
I started learning German in 1999, and for the intermediate level I went to reputable language schools. First, I studied German in Goethe Institute, then in Berlitz, VHS, and then in Institute for International Communication by Heinrich-Heine University, Düsseldorf. After getting the highest scores in almost all parts of the exam for academic German, duration of which was over 5 hours, I was accepted in a master degree program at the Essen-Duisburg University, where I stayed for one semester, before leaving for the United States.
I am a German national who lived in US for over 7 years. In addition to a few business English courses during my university studies, I finished advanced US college courses for English Composition and Critical Thinking In 2014, as well as Business Law, Screenwriting, Documentary Filmmaking, and other subjects, all with GPA 4.00 in San Diego City College, and was on the Dean's honor list. The results were accepted by the University of California, San Diego as a substitute for academic English exam (TOEFL) in my Master of Science application. During my studies I worked as a legal and IT German-English translator.
I am currently fluent in three languages, and I spoke another two in the past. My academic background is in economics (a 5-year university degree), and I am an independent artist (fine art and filmmaking).