The official final words of the European Union to the UK were "thank you, goodbye, and good riddance" after a top diplomat made a joke that was lost in translation.

Irena Andrassy, the Croatian ambassador to the EU, made the declaration to her British counterpart Tim Barrow on January 29 during his final appearance at the weekly meeting of EU envoys.

The UK formally exited the EU on January 31 after 47 years of membership.

Diplomats present in the room told the Financial Times newspaper that Andrassy meant no ill-will whatsoever but that it was a case of missed translation.

Barrow and his team "saw the funny side and understood how it was meant. But history will show that these were the last words from the EU to the UK's ambassador before Brexit," one official said.

However, Andrassy appeared to suggest on Tuesday that she understood the words but meant them as a joke.

"One more thing we share with our British friends — a good sense of humour," she wrote in a tweet that was retweeted by the UK's Mission to the EU.

Croatia, which currently holds the rotating six-month EU Presidency, labelled the translation blunder as a "humorous exchange between friends".

"Croatia regrets, but fully respects the UK's decision to leave the EU and will play its part in negotiating a strong future partnership with the EU," it added.

Trade talks between the UK and the EU are expected to start in March with the UK.

It's not the first time that subtle differences in language have caused diplomatic mishaps.

French President Emmanuel Macron caused hilarity in Australia after describing the wife of then Prime Minister Malcolm Turnbull as "delicious." In French, the word means "delightful" when referring to a person.

Meanwhile, former British Prime Minister Theresa May drew the ire of Moscow with a speech praising her armed forces for protecting "our waters and our skies from Russian intrusion" after local news organisations translated it into "Russian invasion."