所谓流利是从fluency来的，还有两个，accuracy, flexibility，这两个做不到就达不到流利的。如果仅仅考虑词汇量。这段可以参考：
Your vocabulary comprises all the words you know. But this definition oversimplifies the situation. Actually you have four overlapping vocabularies that you use in various situations. First, you have a speaking vocabulary, the words you use in general conversation. For most people this vocabulary consists of the few hundred words they use when talking with friends. Next, you have a writing vocabulary, the words you use when writing. This vocabulary is considerably larger than your speaking vocabulaly, consisting of about 10,000 to 45,000 words. Many of the words in your spoken vocabulary are also part of your written vocabulaly. But certain words like satire, analogy, positron, and logarithm belong almost exclusively to your writing vocabulary. The coloquialisms and slang that are part of your spoken vocabulary are usually excluded from your writing vocabulary. You also have a reading vocabulary, the words whos meanings you know but do not necessarily use in writing or in conversation. Words like plutocrat, elucidate, and equivocate might fall into this category. Most college students have a reading vocabulary of between 50,000 and 100,000 words. Finally, there is your guess vocabulary, words whose meanings you do not know exactly but can infer because the words are similar to ones you already know or because their context gives clues to their meanings.
Beyond these are words that you do not know and that you cannot figure out. These words you must look up in a dictionary. p. 330
Kirszner, L. G., & Mandell, S. R. (1986).The Holt Handbook(1st ed.). New York, NY: Holt, Rinehart and Winston.
追问我现在看英文很吃力，能不能用中文回答？
追答这里说的就是专业级别的水平，慢慢达到吧。一两天是不行的，读懂了中文也照样不等于读懂英文。