Whether or not you need a "certificate" to teach is based on local laws. In the United States, with 50 states, we have, effectively, 50 different laws (there is a commonality to them, so perhaps we really have 10 different laws, but it depends on where you live as to what you need as qualification). For example, in Pennsylvania, I am qualified to teach college level and even teach Master's and PhD programs, but I am not certified to teach elementary school, middle school, or high school. Why? Because the state has laws about the qualifications required for those schools, and possessing a PhD and 60 years of teaching experience are not sufficient. I have to have taken college courses on how to be a teacher from a certified college program.
However, if you are not teaching in a public school, but just offering courses to anyone who is interested, then, once again, it depends on your local laws. I may not call myself a "doctor" or "engineer" or "accountant
unless the state has certified me, but I can call myself a "teacher" and teach whatever I want, wherever want, to whomever is willing to pay me, as long as I am not an employee of the public school system. If, however, I am teaching anyone under the age of 18, I am required to have a criminal record check and a background check, to make sure I am not a criminal or child molester. But if I want to open a school, which has one room (probably rented), and teach Arduino programming, there are no laws that prevent me from doing this. But Vietnam may treat "teachers" like U.S. states treat "engineer" or "doctor", and require that you have some certification in the subject you plan to teach. There may be a government exam you have to pass, or you need to provide some evidence as specified by law to prove that you are capable of teaching. To be an "architect", in Pennsylvania, you must pass two 8-hour exams, administered by the state, given a year apart. So it all depends on your local laws.