I'm not sure what a worthy candidate requires, and things vary- which countries in Asia? I have lived in a few countries here, but know nothing about Africa.
It's hard to say what ages you would be teaching- some schools deal with both, while other specialise. I have very little experience of teaching children.
If you have a bachelor's and a master's, I wouldn't bother with any other qualifications, most intelligent business managers in Asia will hire you on the basis of those degrees. The qualification courses teach things like "prefer complete sentences" and "write clearly", things a very intelligent person will usually work out in any case.
I disagree strongly with your second. The four/five-week course is very intensive and extremely relevant to modern teaching. Your remarks about what they teach are nowhere near the truth. Have you ever seen a syllabus?
My daughter (MA) did a Trinity CertTESOL and my wife (MA, PhD) a CELTA. Both felt that their courses were among the most intensive learning they had ever undertaken and both have said that their first year of teaching would have been an absolute disaster without them.
Maybe it took me a few years to work them out.... But, to explain my thinking while writing this: I taught English in Hong Kong, and was evaluated by a Deputy Principal from Australia. No need to name her, but she was third in rank in one of the Australian States (NSW) in the Ministry of Education, after the Minister and Deputy Minister of Education. She was all about getting our English teachers to go off and do a TESOL course, and had loads of experience in them, including teaching them. After seeing me teach English, she said I didn't need to take one, I was doing exactly the right sorts of things on my own. So, I thought they taught things which were already accessible to good teachers with empathy toward the learner, or some such rationale.
[Edit: I've looked at the link to the Cambridge CELTA, and I agree it has a lot of information; still, I think much of that material would not be 'new' to a B.Ed. graduate with no specific ESL teacher training.]
When I started TEFLing in 1968, very few of us had a certificate of any sort (IH, RSA and Trinity were the names then) and most of us learnt as we went along. I was one of the rare birds who was actually a qualified teacher in the UK, though this did not mean that I knew much about TEFL. Those of us who took the work seriously managed, and our learners didn't do too badly in the circumstances (there was little better available), but I shudder now to think of some of the things that went on in my classroom then. My learners would have fared far better had I had the knowledge of setting up pair and group work, acquired basic elicitation skills, recognised the importance of the four basic language skills, known that teaching was not 90% lecturing to the class, and the many other things that trainees learn on a TEFL course,
The reason that so many schools are insisting on some form of TEFL certificate these days is that bitter experience has taught them that that teachers without an initial certificate (unless they have managed to gain several years' experience) are usually a liability. Most of us know, and Cambridge and Trinity make it clear, that the certificates are only initial teaching qualifications, but they do ensure that people who have gained them have acquired some knowledge of English grammar and phonology and some understanding of how learners can be enabled to learn reasonably effectively. They have demonstrated some level of competence in the classroom.
This is a very valuable and interesting exchange, 5.... thanks to your input. Another thought along my initial lines though: monoglots would probably benefit from TESOL-type training a great deal more than bilingual or trilingual people, who must have lived through years of a successful classroom experience. After having learnt French and Portuguese, teaching English became that much easier to me. But I agree the truth is somewhere in the middle. (Confession: I've always felt, perhaps in an unjustified way, that since "Shakespeare had no Bachelor of Fine Arts in Drama," people who start with a formal course are way behind those who get into something because it has always been a passion, and who thus have already built up an encyclopaedic knowledge about a subject on their own.) Along with a high quality education -- which I strongly support -- but which ought to have trained the mind to be supple and flexible enough to think clearly and make intelligent steps in any area. Oh well, I feel I'm just digging me own grave, and losing the 'debate.'