A Melbourne couple accused of keeping a Tamil woman as a slave for eight years wrote her a letter in English to thank her for her help – but she was illiterate.

The husband and wife, who cannot be named for legal reasons, are accused of intentionally possessing a woman as a slave between July 2007 and July 2015.

A trial began in Victoria’s Supreme Court on Wednesday, where the prosecutor revealed the couple’s alleged victim could speak the Tamil language but not read or write in it, and had no understanding of English.

She had come to Melbourne from her home in Tamil Nadu, in southern India, for two six-month stretches in the early 2000s to help the couple care for their three children.

Mr Maidment said each time the woman came on a six-month tourist visa. After the first stay,  the Melbourne couple wrote her a letter in English to thank her for helping and invite her to return.

“The word thank you does not quite express our gratitude toward you … we are eternally grateful for you,” the letter from March 2005 said.

Mr Maidment questioned the purpose of the letter, noting the victim – a mother and grandmother – was living under the same roof as the couple, travelled with them to India when her visa expired and couldn’t speak or read English.

He suggested to a jury that it was “window dressing” for Australia’s immigration department so the woman would be granted another visa.

Another letter, also written in English and purporting to be from the woman later allegedly held as a slave, said the couple and their children had “become very affectionate toward me”.

It said the couple had visited the woman and her family in Tamil Nadu at least eight times in the previous decade.

“I become more and more close to them each time they visit. They both love me as their mother,” it said.

In his opening remarks, Mr Maidment said it was the Crown case that on each of her three visits to Melbourne the woman “essentially became a domestic servant” to the couple.

It’s alleged the couple had such a degree of control over her fundamental rights and freedoms that it constituted slavery.

Mr Maidment said that included her rights to communicate with others, freedom of movement, and her rights to health care and payment for services.

The woman also became an illegal non-citizen after a third tourist visa expired in August 2007. Her passport expired in 2011, four years before it’s alleged the period in which she was kept as a slave came to an end.

“It wouldn’t take much for you to understand the restriction that puts upon her,” Mr Maidment said.

The trial openings are continuing.

-AAP