"Done." is a completely valid and grammatically correct "sentence." Technically a sentence must contain a subject and a verb, but the subject is implied and understood from the preceding discussion.
"Translation done." is not grammatically correct. At this point, I think it would be expected that you have a verb to complete the sentence. You sort of have to commit to one or the other.
After the comments, I'm updating this to explain why I would not say "Translation done." I've always been taught that "done," as a past participle, should not occur without an auxiliary verb. The exception provided for one-word sentences is accepted by most. But by adding another word without a verb it becomes a fragment, not a special type of sentence. If you find that acceptable, use it!
To me, "Translation done" is no more correct than the following:
"Mission accomplished" is a complete sentence, not a fragment.
None of this is to say that the recipient of your email wouldn't understand what you meant. In an office setting, I wouldn't hesitate using "Translation done." But I would do so knowing it was not grammatically correct.
But to your question, you can use any punctuation available to you in normal sentences.