ITN has found some previous footage:
The footage, apparently filmed in January 2012 at the ANC party's 100th anniversary, shows the man making gestures as Zuma sings to the crowd.

ANC communications manager Keith Khoza told NBC News that the interpreter had translated for party events in the past, but said that the man only “volunteered” and was not paid.
Link:http://www.itv.com/news/story/2013-1...ealed-as-fake/