It’s true there have been one or two notable exceptions to the rule. It was said of Paul Mantoux, who is generally regarded as the founder of modern conference interpreting for his role at the Paris Peace Conference of 1919:
"The official interpreter, Paul Mantoux, interpreted from French to English and back again throwing himself into each speech with such verve that one might have thought he was himself begging for territory." (MacMillan, Paris 1919, p. 54)And in the old film about the United Nations interpreters in New York (Other Voices, c. 1975), one of the interpreters tells a story concerning the famous incident when Nikita Khrushchev took off a shoe at the General Assembly and banged it on the table. A Russian interpreter was so carried away that he too shouted, and banged the table in the interpreters’ booth until the water glasses jumped off. However, the interpreter who tells the story adds, “He was a bit of a ham. He’d been an opera singer before,” as if to underline that it was not the norm.
One might call such behaviour interpreter mimicry.
For the Cameroonian church interpreters like the one I heard there was no such norm. Or rather, the norm was reversed. The experience left me inclined to say, in imitation of Pope,
For norms of interpreting let fools contest;
Whate’er makes most compelling speech is best.