Grammar Point:
The sentential 了 often appears in sentences with adverbs, indicating that something will happen soon. It suggests an imminent change of state.
Before you read this post, please make sure you have known what is 了1, 了2, and 了3.
If you are not sure about it, you can check this article: 了 Part1
了2 (Sentence particle 了) different usage
快 kuài / 快要 kuàiyào / 就要 jiùyào / 要 yào + V + 了2
It indicates that the situation is about to change soon.
By adding any of these four adverbs – 快 Kuài, 快要 kuàiyào, 就要 jiùyào, or 要 yào – into the sentence, along with the use of 了2 to indicate a change of state, it implies that the situation will change soon.
他的生日快到了他的生日快到了
His birthday is coming soon.
他要睡覺了他要睡觉了
He is going to sleep soon.
就要吃飯了就要吃饭了
It’s almost time to eat.
中文課快要開始了中文课快要开始了
The Chinese class is about to start.
我明年就要回國了我明年就要回国了
I will be returning to my home country next year.
However, 快 kuài and 快要 kuàiyào, cannot be used if there is a time word present.
我明年就要回國了我明年就要回国了
I will be returning to my home country next year. ✅
我明年快要回國了我明年快要回国了
I will be returning to my home country next year. ❌