I have a brief that vocabulary should be placed in the first place for proficiency. I had a chance to talk with one lady who had just started her life as teacher of English in high school. Her English is fluent and her response is good. She has gone abroad to study for 4 years. She seems to be proud of her English. It's no doubt that her English is better than me. But I could find the room to have a slight edge in. Those are vocabulary and natural expression, I believe. I noticed her vocabulary in her English is quite limited. She doesn't know even "pollution". Hmm, it might slip her mind, may be. How about "wear the pants"? When we talked about the dress code in her school, I said she might wear the pants in her school. I intended to just play a joke on her. But she had no sense of humor. Essentially, she doesn't know the real meaning. One native English speaker hearing our conversation gave me a wink. Besides,when I asked her about her new start as a teacher of English, I used the expression, "What springs to your mind about new start in your life?".
She) Spring?
Taka) Yep
Taka) What springs to your mind about new start in your life?(Slowly)
She).........
Taka)What do you think of new start in your life?
She)Aha! well I think bra bra bra ...(She starts to express her idea)
Now my English is far below her English. But I have a confidence that I can catch up with her. I won't be beaten.