I believe if a work is translated, both copyrights of original author and of translator should apply. Is that correct?
Yes, both apply to the translation.
If so, then probably a year for each should be entered.
Yes. But that already done in Wikidata (and in most of the cases the date of death is more important thant date of publishing).
For VIAF, there is entries for both works and edition (called « expressions » like in FRBR), qv. https://viaf.org/viaf/178622639/ (work) and https://viaf.org/viaf/175353827/ (expression). For Romeo and Juliet, there is around 222 expression of the work in VIAF.