Canadian prime minister Justin Trudeau stepped in to save the day after Eurocrat Jean-Claude Juncker's words to world leaders were lost in translation during the G20 summit in Hamburg.

The European Commission president appeared to have problems pressing the right buttons on the system that allows translators to relay his words in the many different languages spoken at the summit.

But the Canadian premier was quick to jump-in to resolve the technical difficulties, allowing Mr Juncker's words to be heard loud and clear.

A western diplomatic source said the repeated failure of the translation system and headsets "kicked in particularly" when the commission president rose to speak.

They added: "He had to stop and wait for a long time as it was going on and off.

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"Eventually the man who rode to the rescue was one Justin Trudeau, who intervened to explain exactly what buttons he had to press at what stage in order that his comments would be translated in the correct languages.

"The same problem hit when the South Korean leader was talking and (Angela) Merkel, who at this stage was very amused by the whole enterprise, turned to Justin Trudeau and said 'Justin, you're the only one who understands this', so was instructed to help fix it."