Which is the best certification to obtain in order to teach English as a foreign/ second language?

I recommend2 certificates: the first in English Language and literature and the other in TEFL

IELTS Proficiency Advanced

For non natives, it is important to prove your competency in the language. For this reason you should take the Cambridge Proficiency Exam. In my opinion, it will show that you truly understand and can master the language. To learn teaching techniques, the most widely recognised qualification is the CELTA but there are also others. The important thing is to give yourself the best chance of finding work, the course should be of at least120 hours duration with6 hours of assessed teaching practice. This is the minimum criteria for those wishing to work in an accredited school in the UK. A DELTA is the next step and this qualifies you to become a Director Of Studies. I would also recommend more senior teachers to take this course as it gives additional skills in the classroom and opens many doors regarding career development.

1. A high band score in IELTS or TOEFL (for non-native Teachers)

2. A BA in English Language (and Literature)

3. CELTA

You should be fun energetic and patient. help yourself with games or crafts bacause they love them also use songs and outdoor activities if you can.

The students' result whom one  has English language is the gauge to certify the teachers performance

1- TESOL

2-TEFL

3-CELTA

4-DELTA

5-PCELT

there are many Certificates such as:

TESOL =teaching English as second language

CELTA

PTP.

.

If you already have a bachelors degree then a CELTA certificate would be a good place to start. Your other options would be a bachelors in English literature/linguistics etc or a bachelors/masters in TESOL. Ideally a bachelors or masters in TESOL would be an advantage. I hope that helps

It depends on the purpose for which it is assigned.

My opinion: an educational establishment in which one is going to obtain some certification

should be accredited (or at least, recognised) in the country of interest

and have direct connection (contract) with a "native or mother" establishment in England (optionally - any reputable establishment in any  English speaking country -US, India, etc.).