I am Danish. In high school, I learned my Danish grammar, English, German, and later a little Russian. I speak and write English,speak German fluently (but never wrote a lot), and I speak some Spanish plus a little Mandarin.
Two years ago, I was teaching English to three (one-on-one) Chinese school kids in Beijing for two months. They were 13 years old. They had learned much English at school, but I could hardly make them say one sentence of their own. After 2 months, I could hardly stop them talking.
I found many years ago, that I am a nature talent at teaching one-on-one. I identify the hurdles that keep my student from progress. We work together. I respect human limits (25 minutes lesson, 2-3 minutes physical moves, 25 minutes lesson) for concentrated brainwork. I also help you find the right tongue position for articulation. E.g., Chinese have severe problems with "r". I give you the special solution/training. In each lesson we repeat the main issues that are very important. Language learning is repetitive... And we keep the lessons simple.
Last summer, I was helping my Afghan neighbor with his homework and pronunciation in Danish. He was so afraid not to pass his exam. But he ended up as one of the best in his class.