"请保持安静。"

Translation: Please keep quiet.

[PeaceJoyPancakes]

"Quiet, please." (On a sign, for example.)

[NasuSamaruk0]

Yes, that is also acceptable.

[MicahLiuba1]

Cannot "please be quiet" do?

[Bjorn605462]

I tried the same, rejected. Hope a native Chinese speaker could comment on this.

[PiFi700860]

Would 'Please remain quiet' be accepted as well?

[K8Y8Sister]

"Please be quiet" should be accepted... you ask people to "be quiet" not to "keep quiet".

[SLs7NEi5]

How about "Please keep in silence"? Shouldn't be?

[PiFi700860]

No, shouldn't be.
'In silence' is a condition, it describes something else. You can work in silence, for example. So, with 'keep' it doesn't work, as 'keep' requires an object, adverb or verb to describe, which 'in silence' isn't.

[K8Y8Sister]

still your sentence is unnatural.

[K8Y8Sister]

unnatural sentence... maybe you meant "please keep silence"?