To introduce a sentence that contradicts or contrasts with the previous sentence, start it with "However,…" This will alert your reader that a shift is forthcoming. Always put a comma after the "However," and follow it with a complete sentence.  You might write, "I was very excited to be invited to lunch. However, I had already made plans." Another example could be, "The pattern was certainly original. However, the new wallpaper did not match the furniture at all." When you have two full sentences that are in opposition or contrast to one another, but are closely connected, join them with a semicolon, the word "however," and a comma. This shows that the second sentence is in opposition in some way to the first.  Start with two sentences that contain opposition: "I would love to join you for lunch. I am too busy." Join them in this way: "I would love to join you for lunch; however, I am too busy." This will make the connections between the sentences obvious, and help your writing sound more cohesive. To interrupt a sentence that is already in progress, insert "however" between two commas. Like other uses of "however," this implies a contrast to the previous content, but in a way that makes the contrast sound a little less crucial.  Put ", however," after the subject of the second sentence: "I can't make it to lunch. You, however, are going to love that restaurant." Use it to divide a two-part verb: "I can't make it to lunch. I could, however, join you next week." Put it at the end of the second sentence: "I can't make it to lunch. I could join you next week, however."

How would you rephrase that briefly using Chinese?
用“However”作为一个对比语句的开头。 用“; however,”连接两个对比语句。 用“, however,”作为题外话。