I agree with Norman. Language teaching methods have changed in the last 100 years. The old emphasis on grammar and vocabulary has been replaced by an emphasis on using the language. Of course, some grammar and vocabulary are required, but they have a smaller role than in the past. My in-person French and English students (usually children) do daily reading and listening to stories at progressive levels (A1-A2-B1). During lessons, we talk about their lives (last week and next week). My student become fluent at the B1 level (1000 common words plus intermediate grammar) in 12 to 18 months.

I just want to agree with Norman. You don't learn languages with dictionaries. While I don't speak another language very well yet, I know a lot of bilingual people and they all learnt by not trying to complicate things by adding in words they really don't know how to use. You don't learn about other cultures by buying an atlas. Most fluent english speaking people (including natives) don't actually have a very large vocabulary. They just know the most common words and over time got better at using them.

Thank you very much, Norman, your tips are quite helpful to me! And I mean I might need a English dictionary what using English to explain words, not English-Chinese dictionary. Thanks again.