Level 6 is usually for native or pretty darn near native speakers.
Spanish: Librería = English: Bookstore
Spanish: Biblioteca = English: Library
I have friends who are non-native speakers of English who achieved a level 6, but it often involved moving to an English speaking country for at least two years and learning the language by living it everyday. I speak several languages, and speaking by experience, with a book only you won´t speak level 6.
I recommend that you have a look at the grading criteria...
ICAO Language Proficiency Rating Scale