Like many others in this thread, Ifm assuming that when you say youfre a teacher, you mean youfre currently teaching in some country other than Japan, and that youfre thinking about looking for a job as an English teacher in Japan.
If thatfs correct, I would say no, I do not think an English teacherfs salary is enough to support a child in Japan.
Again, Ifm assuming that when you say gan English teacherfs salary,h youfre referring to the average salary foreigners make working in Japan either as ALTs (assistant language teachers in elementary, middle, or high schools) or as eikaiwa (English conversation school) teachers. As mentioned, starting salaries for such positions are usually about 250,000 yen a month. In Japan, this is usually enough money for a single person to afford a modest lifestyle. A modest, one-room apartment will generally cost between 50,000 and 100,000 a month, depending on location, age of the building, and other factors. That leaves somewhere between 150,000 and 200,000 yen a month for everything else, and by the time you pay for other expenses (utilities, groceries, taxes, insurance) therefs not a whole lot left over for entertainment or savings.
As a single person working as an ALT or eikaiwa teacher, you wonft be living in poverty, but therefs probably not going to be enough money left over to properly care for a child. Also bear in mind that for ALT and eikaiwa jobs, there is little chance of getting a raise or promotion, so a plan of you and a child living on a shoestring budget until you climb the ladder at work and start making more is unlikely to work out well. ALT and eikaiwa jobs also rarely provide much in the way of benefits. Bonuses arenft paid, and while some may offer basic health insurance or rent support, others offer no benefits at all.
Another thing to consider are childcare costs. If you are working as an ALT, you will be working when children are in school, so you will need to obtain childcare for your child if they are not yet in school themselves. Childcare needs/costs will be even higher if you are working as an eikaiwa teacher, since eikaiwa shifts are usually weekday nights and weekends.
Add up all those factors, and trying to raise a child on an English teacheres salary would require an extremely spartan, and likely unhappy lifestyle with near-constant money worries.
On the other hand, if by gan English teacher's salaryh you mean the salary for English teachers at universities, international schools, or military bases in Japan, those salaries vary widely by the exact position/school. Some of them may pay enough for you to support yourself and a child, but the number of available jobs is much lower, competition for them more intense, and the professional requirements (years of experience, certifications, etc.) higher.
Last, from the way your question is phrased Ifm assuming that youfre not currently living in Japan, and are thinking of moving there to teach English. That would mean either adopting a child in your home country and moving to Japan together, or moving to Japan by yourself and then adopting a child there. While Ifm not a child psychology expert, I would imagine those who are would recommend against either plan. Moving to a new country and adjusting to your new lifestyle, even in a country youfve researched extensively and feel a strong attraction to, is a challenging and stressful process. Likewise, adjusting to a new family is challenging and stressful for an adopted child, even if the adopting parent is loving and committed. Combining those two processes at the same time is likely to place excessive difficulties on you and your adopted child, so it may be best to handle them one at a time instead.