let's call it a day!
今天就到这儿吧！

“今天到这儿吧” 还可以怎么说呢？
I think that's it.= We're done for the day.

“我请客”怎么说？
Let me buy you a drink.
Could I buy a drink?
I'm buying.
Drink is on me.

We probably should call it a night.
我们可能要结束今晚了。
Call it a night
结束今晚的工作；该睡觉了