Which is correct English my teacher of English or my English teacher?

"My English teacher" would be better, but it would not be completely wrong to use the other way.

Use "my teacher of English" if specifying the subjectbeing taught. Like 'my teacher of Geometry' or 'my teacher of History', these can also be expressed as 'my Geometry teacher' or 'my History teacher' with no loss of meaning.

Use of "my English teacher" is simpler and could be used if there is no confusion over nationality/cultural background. However, for comparison consider, "My English teacher of Geometry was difficult to understand". Or, if the context has been established previously then, "My English teacher was difficult to understand". This would mean someone from England or who spoke English as their base language and does not refer to the teaching of English. As opposed to "my teacher of English was difficult to understand", which specifies the subject being taught.

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Actually, the correct terms can either be one of the following:

1. My English teacher, or

2. My teacher in English

It never was, or will be, the preposition, of.

Rewritten, that will become:

"My English teacher speaks very eloquently." OR

"My teacher in English speaks very eloquently."

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Never?

The Shorter Oxford English Dictionary, 1973, p 2251, for its definition of 'teacher' gives the example:

A t. of anatomy 1799.

I take this to apply to the teacher of any subject. e.g. teacher of geometry, teacher of English etc.

I don't dispute that in could be used but disagree that it is any more correct than of in this context.