The definition of fluency in a foreign language

When can I say that I speak my target language fluently?
This question is the one which foreign language learners always ask themselves and never get answered. I've been asking myself WHEN WILL YOU SPEAK ENGLISH FLUENTLY [ I want a word to emphasize my sentence, but don't know which one suits here, and this is the most frustrating thing about learning a language] after learning it for more than 10 years?

I sometimes get so frustrated that I just want to stop learning English, but I want to speak it better, understand it better, and communicate with people better. One thing I am really grateful about is that English is spoken by so many people and I can communicate with people from other countries, even though our mother tongues are different.
Thank you, English. I hate you for not being easy, but I love you because you helped me know other people all over the world, and I will keep trying to understand you better.