The 24-year-old went to that country in February 2021, learned Japanese and then enrolled in the Japan University of Economics.
He was allowed to work part time for a maximum of 28 hours a week, from which he could earn around ¥150,000 (US$1,120) a month. So he worked as a waiter in a restaurant in Tokyo.
But since his parents had to borrow money to cover his tuition and living expenses, he wanted to work more and send some money to them. Through an acquaintance he managed to get a job as a manual worker at a fruit factory, and worked another 20 hours a week for VND25-30 million ($1,054-1,265) a month.
He was paid in cash, and promised his employers not to tell tax authorities about the job and thought "no one would ever know."
But when his visa expired during his freshman year in January this year, he was told he had to leave Japan for working more than the number of hours allowed.
Like Dung, many Vietnamese students in Japan and South Korea are working more than the maximum number of hours allowed or at illegal facilities to earn extra money to cover their expenses and clear tuition debts. But the violations put them at many risks, including of deportation.
Dung has since returned to Vietnam, but is staying with a friend and does not dare go back to his hometown for fear of his parents’ reaction.
He says: "I never thought the door would be closed shut like that on my career. I haven’t even paid back all my debts."
Le Hung, 20, a student in Busan, South Korea, had been working part-time at an unlicensed facility that manufactures cotton swabs for Covid-19 tests since early 2020. He got VND26 million ($1,091) a month for his work, but did not have a labor contract.
The facility was located in a remote rural area, and so Hung and other workers would often gather at a location to be taken to the site by car.
One day, as the workers got into the car, police officers arrived to check their papers. Hung had to pay a VND40 million fine and was prohibited from working part time for a year.
In March 2021 he signed up for a part-time job again, this time at a factory that processed agricultural products in Gyeonggi. He worked 40 hours a week while regulations only allow international students in university to work 20, and was caught by the police for a second violation. They reported him to the school, and the school did not bail him out since he also frequently skipped classes.
Hung was eventually deported to Vietnam.
Not worth it
There were 38,600 students in Japan as of 2022 and 60,000 in South Korea.
Tuitions and living costs for a foreign student come to VND244-370 million a year in South Korea and VND370 million in Japan.
Some 75% of foreign students without scholarships or financial aid in Japan support themselves with part-time jobs, mostly in restaurants and convenience stores and translation and teaching, according to information site Study in Japan.
Over half earn around VND178,000 an hour.
A Vietnamese student in South Korea says his compatriots typically take part-time jobs in Seoul and neighboring areas at restaurants and diners for around ₩9,620 ($7.42) an hour.
Financial pressure, or simply a desire to earn more money, sees many of them work more than the number of hours they are allowed to or at unlicensed facilities without labor contracts.
Kim Manh Hiep, a teacher at the Midream Japanese language school, says companies look for part-time workers for one to three months without giving them labor contracts. While they promise workers not to report them to tax authorities, they often do it anyway to get tax relief at the end of the year, he says.
"There have been many cases of students seeking a visa extension only to discover they have worked past the number of hours allowed and can no longer stay in Japan. It would be too late for regrets at that point."
In South Korea, international students working at unlicensed facilities are often forced to take wages that are 20-30% lower than normal. Some employers even cheat the students out of their money.
Kieu Chinh, 32, a consultant at the Law Win law firm in South Korea, says she has seen several cases of students not getting paid for their work.
"There was someone who worked part time at fast food restaurants and had a month’s worth of salary, of about ₩700,000, being withheld. They were eventually paid only ₩300,000."
These students also risk their health from occupational hazards since hospitals do not admit them if they do not have proper personal documents.
Thich Tam Tri, a nun at the Nisshinkutsu pagoda, says: "As head of the Vietnamese Buddhist Association in Japan, I have been the guarantor or interpreter in cases where international students suffered severe workplace accidents and no hospitals were willing to accept them."
Chinh says working part time while studying abroad is a way to support oneself and gain experience, but students should choose their jobs carefully and avoid those at construction sites and karaoke parlors since international students are not allowed to work at such places in South Korea.
Hiep says students should not be too "greedy" and work more than the number of hours allowed.
Moreover, an international student in Japan earns around VND400-600 million a year after graduation, he points out.
"The money one can earn in a year is equal to the cost of three years of studying with enough to spare to pay back debts."