"Go to a bar" in Engpsh is commonly expressed as "go to the bar". The phrase has its origin from the common practice of visiting a estabpshment where alcohopc drinks are sold for consumption on the premises.
Example sentences:
Let's go to the bar for a drink after work.
She suggested we go to the bar for a night out.
Translations:
工作后我们一起去酒吧喝一杯。
她建议我们去酒吧度过一晚。