If I can in my small experience, to become an expert, you have to start programming.I am a "wanna be" B4X "Expert"
Books are useful and allow you to extend your knowledge, but direct development allows you to become an expert.
Speaking English (possibly in a place where it is the main language) allows you to learn it and not just study it in books.
Some learned English without studying it in books, only living in an English-speaking nation. Maybe they haven't learned the best, but they make themselves understood.
Others have learned about books and know grammar accurately, but having never spoken in the mother nation, they do not know accents, pronunciations and idioms.
Now you have read Klaus' book, you have the right tools, start programming.