Making up around one quarter of the nation's total population, many migrant workers are constantly switching between their native language and English.
Evelyn Faura migrated from Argentina 15 years ago, and initially worked in a factory where she didn't need to constantly translate technical terms.
Listen: Michael Kenny reports on the new findings.
Now in a law firm, she said her working life was lot more stressful.
"I think the most challenging thing is that when people are expecting you to make a decision, to fix something right there and then," Ms Faura said.
"You just have to react and make a decision without having that luxury of being able to process that in my own language."
It's a similar story for Mexican robotics engineer Santiago Forseck, who settled here two years ago.
Mr Forseck's completing his doctorate and finds it hard shifting between Spanish and English.
"Actually a lot of the terms, there's no way to translate them," he said.
"So the process, the mental process of working in robotics, I tend to do it in Spanish while trying to word it in English.
"When I was talking to my thesis supervisor, it was really stressful trying to explain to them my ideas on my project and thinking in Spanish and translating into English."
Australian and German researchers have found speaking a foreign language in the workplace directly impacts on brain capacity.
The joint study was conducted through the University of Sydney and the University of Tuebingen.
It found speaking a foreign language weakens the neural activity in the areas of the brain that house working memory.
In the workplace, that extra brain strain can cause more stress and make it harder for employees to think laterally and manage difficult situations, according to lead researcher Stefan Volk from the University of Sydney's Business School.
"A foreign language is processed in a different part of our brain than native language is," Dr Volk said.
"So a native language is what we've learned before the age of five. This language is typically processed in the automatic part of the brain. So we can use and comprehend and operate in our native language without investing significant mental and cognitive resources."
To overcome that added stress, the researchers said employers could give these workers more rest breaks.
Dr Volk said they could also encourage the workers to take a walk in the park or go for a meditation session - or simply get something to eat or drink.
"Glucose, which is essentially sugar, is brain fuel," he said.
"So the worst thing you can do is to work in a foreign language, engage in extensive multi-tasking and to be hungry because these are three factors which all are tapping into these limited cognitive resources.
"Obviously very often you don't have a choice. You have to work in a second language. You have to multi-task, but being hungry is completely unnecessary."
