Auckland Mayor Len Brown was advised by his former mistress Bevan Chuang to speak English and not to try speaking Mandarin on an official trip to Hong Kong, papers show.
"Please do not say 'ni hao' [hello] or 'xie xie' [thank you] in Hong Kong, as this is Mandarin and this will make Len look foolish," she told mayoral press secretary Melanya Burrows.
The mayor's then-lover offered the advice two days before Mr Brown flew out to China and Hong Kong on a New Zealand Transport Agency trip to study big infrastructure projects in November 2011.
Official documents about the four-day trip were released to the Weekend Herald last night under the Official Information Act.
They back up the findings on an EY (formerly Ernst & Young) investigation which raised concerns about a "private" and/or "personal" dinner Mr Brown had with an interpreter at the Okura Garden Hotel in Shanghai on November 11.
An email on November 10 shows the Transport Agency was not comfortable paying for the interpreter's cost at the dinner and Ms Burrows was instructed to "discreetly arrange to pay for her meal".
A mayoral spokesman said there were three people at the dinner - Mr Brown, the unnamed interpreter and Ms Burrows - where they discussed what was coming up on the trip.
Ms Chuang did not go on the study trip, but the documents show that as a member of the Ethnic Peoples Advisory Panel she provided some "side notes" for Ms Burrows and the mayor.
Hong Kong-born Ms Chuang said the region spoke English and Cantonese, and the official language was English and "traditional" Chinese.
"Most of the delegates will be able to speak English and I would not expect them to bring a translator with them (even my grandmother says 'hello' and 'bye' in English, and she is 93 years old!)," said Ms Chuang.
She provided advice during a two-year affair with Mr Brown - which ended in July last year - whose political career took a tumble when his extra-marital activities were made public on Cameron Slater's Whale Oil blog three days after last October's local body elections.
Mr Brown, who is married to lawyer Shan Inglis and has three daughters, has rejected calls to resign, been investigated by EY and cleared of using council resources, censured by councillors and stayed on as mayor.
He is taking an overseas holiday with his family next Thursday and returning to work on October 14.