Do you think that only English teachers can teach English or any one of any specialization and good in English can teach it?

I believe it has nothing to do with being an English graduate or an English teacher.
Teaching English needs you to be skillful in English first and then skillful in teaching as well..
This is the general rule.
But being an English teacher for specific fields (translation, literature, ...etc.) I think it needs a very expert teacher not just someone who knows English.
because English of daily life differs from the professional English.

I've been an English teacher for more than two years, I've taught it in language centers, in private classes and in Schools ....
But i'm not an English graduate !

Not only the English teachers, but the qualified English teachers are the ones to teach English.

I think any one of any specialization and good in English can teach it

from experience I can say that ,talent plays big part in tutoring

If you know the teaching methods and have a good English along with willingness to learn side by side you will definitely enjoy teaching English. Rather I would like to say that you may prove yourself a better one than a qualified English Teacher.

There are basically two forms of English:  Colloquial and Formal (grammatical), the former being day to day English (conversational) and can be strongly influenced by region, dialect, slang etc. The second is grammatically correct English, sometimes referred to as the Queen's English and would be used in business, writing letters, composing CV's etc. Formal English would be used in TEFL as it is the basis for learning the language "properly", Colloquial English is generally "picked up" by mixing with native english speakers.

I have no qualifications to teach english but as a native english speaker and a former military Instructor, I am very confident in my ability to teach the subject, both "Formally" and "Colloquially".

Each subject or learning area has its technicalities and language. I speak good English but that does not necessarily make me someone that can teach English,. But, if I can learn the technical skills and didactics that go along with teaching English and develop passion for it then, may be, yes anyone can teach English.

your skills matter alot.
not all English qualified are good teachers.
I myself am a student of Economics but have been teaching English....& quite effectively i guess :D being a learning experience for me too.

From my experience and others' I do agree with Sema Farhoud.

In the issue of teaching, talent plays a big part, and I'm for the saying: Teacher are born; they are not created! Thus, I can say that a person from any discipline can teach a language well if he understands its features and measures, provided he is talented in the teaching process.

I think it has nothing to do with weather you're an English teacher or not.
I've always known that language is something you learn from birth plus language implies early experience.
For example, I have a friend who studied engineering all five years of his life, but apparently had some experience watching movies or other stuff.,So when it came to TOEFL or IELTS he beat me up (I'm a graduated English student).
After all I think that standardized tests are the ones to really measure your ability.
Hence I would say that It depends on your early passion of English or if you were lucky to have a mom or nanny speaks English before your3rd year.