Asylum seekers flown from Nauru to Taiwan for medical treatment have complained to lawyers that language barriers meant they were unable to give informed consent even when the overall quality of care was good.

Australia signed a memorandum of understanding with Taiwan in 2017 to provide medical treatment for asylum seekers detained on Nauru, in an effort to prevent people indefinitely detained on the island from applying for a medical transfer to Australia.

The agreement was disclosed by a Taiwan representative in a letter to the Guardian last month, following a report about an Iranian woman and her son who were transferred to Taiwan so she could undertake life-saving heart surgery, and confirmed by the Australian government overnight.

The woman, Fatemah, had told the Guardian her 17-year-old son also required medical treatment for severe mental illness caused by his time in detention but did not receive treatment before the pair were returned to Nauru. Taiwan authorities said he was not listed as a patient on the medical transfer form.

Taiwan is also not a signatory to the 1951 Refugee Convention, meaning refugees cannot apply for asylum to prevent them from being returned to Nauru.

The human rights lawyer George Newhouse, from the National Justice Project, said that while the Taiwan medical system was of world standard, language barriers between detainees and medical staff, which often required the use of two interpreters, meant some asylum seekers felt they had not been able to give informed consent.

The federal court ruled this month that hospitals in Taiwan also did not have the expertise to perform an abortion on a woman held on Nauru who had undergone female genital mutilation, and ordered that she be brought to Australia for treatment at one of two specialist clinics at the Royal Women’s hospital in Melbourne or at Sydney’s Westmead hospital.

“They are not equipped to deal with mental health issues, cases where female genital mutilation is involved, and the language difficulties make obtaining informed consent extremely difficult,” Newhouse told Guardian Australia.

“Many asylum seekers complain that they didn’t understand the procedures that are to take place and are frightened of what might happen to them. There’s also no proper medical follow-up when they return to Manus and Nauru.”

At least 330 refugees and asylum seekers, including 36 children, remain in detention on Nauru and have been told by the Australian government that they will not have any future opportunity of settling in Australia or New Zealand.

Australia has previously allowed seriously ill detainees to be brought to the country for medical treatment, often after being forced to do so by a court order.

Newhouse said the agreement with Taiwan aimed to circumvent that process.

“The primary objective is to avoid bringing the asylum seekers to Australia at all costs, even if it results in harm to the individual,” he said.

A spokeswoman for the department of home affairs said the agreement was part of the Turnbull government’s commitment that asylum seekers held in offshore detention would not gain entry to Australia.

“The government has been clear that people subject to regional processing arrangements will not be settled in Australia,” she said. “Medical transfer is not a pathway to settlement in Australia.”

The department said Taiwan had a global reputation for high quality medical care and was consistently ranked as having some of the best hospitals and medical technology in the world.