Teaching ESL is a mixed bag depending on what country you target. In some countries it’s a refined, streamlined endeavor where employers seek qualified and experienced teachers and the government has mandatory guidelines as well. To obtain a work visa in a certain country, a government may actually require a teacher have a TESOL certification and/or a certain amount of experience.
In other countries, this isn’t always the case. In China, it’s a little bit of both it seems.
There were once days in places like Korea and Japan where anyone could roll off a plane and be offered a teaching job on their way to their hotel. Those days are over in some countries, and many others are following suit.