"What did we do last night?"
No need in "了" to indicate Past if there is already an adverbial modifier of time ("昨天晚上") indicating Past.
I do strongly agree that it's not a must in Chinese to add 了 to indicate past tense.
I wrote "我们昨天晚上做什么了？" In my six years of learning Chinese, I never understood the proper placement of the 了 (le) particle. What are the rules for this?
I think it is not necessary to say LE as there is already a past tense there.
了 has a LOT of usages. In this case, 了 immediately follows the verb to form the past tense.
干什么 should be more correct than 做什么，and much more natural for chinese speakers. Please allow both...
Can you say 昨晚 instead of 昨天晚上 or is that not legit? It was marked wrong for me but I wasn't confident enough to report it.
My mind had a brainfart and I've translate "last night" as "上个晚上”. Is it wrong, or should it be accepted? I'm really not sure...