A 2000 QBD case involved the question of double interpretation, that is, interpretation from English to Bosnian Romany by way of Serbo-Croat (if that’s still its name). Here is the complete summary from David Swarbrick’s superb site:
bq. Regina -v- West London Youth Court, Ex P J – QBD – 02 August 1999 – Criminal Practice
lip – When absolutely necessary, it was permissible for a court to allow and depend upon double translation for a defendant. A court offered either double translation or a translator who felt 80 per cent adequate in the language of the defendant. A translator must be impartial (never the appropriate adult), and qualified and fluent. The standards required at interview were also required at trial. There must be a natural understanding between the accused and his interpreter, and the next and the court.
[02 August 1999 – Times ]
bq. 4. The possibility, therefore, arises of a process known as “double translation”: interpretation from one language into a second language, and then from the second language into a third language. The magistrate ruled that double interpretation can never be lawful. We are told other tribunals, from time to time, have ruled differently; views are divided. This question is, therefore, one of some general and growing importance and both sides invite the court to take this opportunity to provide guidance.
5. I recognise, of course, that such views we express will necessarily be obiter. Nevertheless, given that we have enjoyed the luxury of research and submission by two leading counsel on what is now an uncontested challenge, it would seem churlish to decline the invitation. I hope our observations may provide some assistance in the future.
I’ve normally heard this process in writing called relay translation (e.g. getting a translation from Maltese to Latvian by way of English, for example).