The Supreme Court in this case laid down procedural guidelines for the use of interpreters in trials in the future . Those procedures had not been followed in this case. At  the Court said:
Another interesting feature of this case is that the appellant has succeeded in establishing a rigorous procedure for future cases but not his own. The question for the Court then became, notwithstanding the departures in this case from the new standard was there any defect that resulted in an unfair trial here? The Court does here exactly what the Crown had "unsuccessfully" submitted it should do at  quoted above. But it does that by using the "required standard" analysis.
Failure of the appellant here was not surprising, because his counsel could not demonstrate any instance where failure of accurate interpretation impeded the conduct of the defence at trial . Of course it would be difficult for counsel to do that here, as the words used by the interpreter were not known. On the facts, however, the defendant had at trial expressed no concern over the adequacy of the interpretation – but then, how could he know what was adequate?
In appeals like this (rape) there might be a public perception that the Court would do everything it could to avoid a retrial. Fortunately for the public perception of the administration of justice there seems to be sufficiently careful scrutiny of the circumstances in this judgment to put such concerns to rest.