The answer in English law is very simple. A translation is itself an adaptation and therefore has its own copyright. It is also a reproduction and therefore if the original is in copyright permission of the copyright owner is (subject to the usual exceptions and defences) needed to make the translation. If both the original and the translation are in copyright then (subject as aforesaid) reproducing the translation requires the permission of the copyright owners of both the original and the translation. If the original is not in copyright then the translation cannot infringe copyright in the original. A fresh translation of the original does not copy the translation so does not infringe the copyright in it.