The real constraint, stated plainly
Some countries — South Korea and Japan among them — write native-speaker passport lists directly into their work visa rules. If you don't hold one of those passports, that specific route is closed to you, no matter how good your English is. This isn't fair, but it's the law in those places, and no course or certificate changes it.
Outside those markets, though, hiring is often about ability and paperwork, not birthplace. Vietnam's private language centres, Cambodia's international and bilingual schools, Thailand's smaller academies, and Mexico's language institutes regularly hire strong non-native teachers. Online tutoring platforms are even more open, since demonstrated fluency and a good camera presence often matter more than a passport stamp.
