C1 level implies the ability to freely navigate the language, understand most grammatical structures and easily use them in your speech. You can easily understand conversations and catch the main ideas and keywords from the first time. You can conduct a dialogue on any topic, expressing your opinion, using synonyms and various constructions, as well as explaining the subject of discussion from different sides, to name pros and cons.
You can correctly use inversion in speech without harming the meaning of the sentence, and use such a technique in order to create a conditional assumption. You do not feel difficulty in speaking, you speak a foreign language on a par with your first language, build sentences taking into account the necessary semantic and logical accents, and resorting to the help of intonational pauses and emotionally colored phrases and expressions.
You can write not only essays on abstract topics, but also reports, book or movie reviews, you are able to argue your point of view. You can read fiction or adapted stories, understanding them without resorting to a dictionary or feeling difficult as you read the book.
C1 is the level of language proficiency, spoken by linguistics graduates, philologists, and translators, i.e. it refers to professional rather than amateur knowledge of the language. This level is considered sufficient for living in the country of origin of the language.