The short answer to this question is never, and I shall illustrate this by explaining how I tackle my long-term project: the translating of the entire poetical works of Lucebert. Once I feel that the translations are as complete and as correct as I can make them they are simultaneously forwarded (a collection at a time) to an expert in the Dutch language and to an experienced literary translator. These two men, who do not know each other, deliver their independent handwritten comments and feedback on the hard copies I supply. I then go through all the poems again in the light of their suggestions. After that revision phase, the whole collection goes on to the professor and Lucebert specialist involved in the project. She goes through everything with a fine-tooth comb. That produces another battery of comments and sometimes some pretty hefty discussions as well. Once that has been processed, I call the translations ‘complete’, but deep in my heart I know that as long as future readers of these translations have significant and valid points to make about the word-choice, phrasing and so on, the work can never really be termed complete or finished. It has also occurred to me that the fourth and final volume might require an epilogue or afterword highlighting matters that have only come to light after the first volumes have been published. In one respect, one can speak of completeness from the point of view of being fairly content with the version produced at the time it goes to print. In another respect, as long as another translator, language specialist or enthusiast can improve on things it is doomed to remain work-in-progress and thus incomplete.
Full interview, and lots of other interesting links, HERE