As an adaptor, I've added a few things to reflect this poem. For example, the rocking chairs that are on stage at the end of the second act slowly and inexplicably begin to rock - these are the remains of the children. These ashes will be falling like rain throughout the entire third act. Generally, a translation is written by someone fluent in the original language. An adaptation like Brustein's is often completed with the help of a native speaker.
Adaptors give themselves the liberty of straying a bit further from the literal translation.
But the line between translation and adaptation is often fuzzy. Any translation is itself an interpretation, marked by its author's time, place, and idiosyncrasies. This inevitable interpretation can be exciting, for it offers a fresh perspective on a play - a perspective achieved only through foreign eyes and ears.