رايكم ايه:He is an English teacher.

[ابو بيشو]

كيف نعرف ان كان معنى الجملة هو مدرس لغة انجليزية او هو مدرس من انجلترا(انجليزى الجنسية)
He is an English teacher.

[الاستاذ خالد زلط]

If"English"is used as an adjectival noun, it means that he is a teacher of English
If"English"is used as an adjective, it means that he is a teacher from England.

[ابو بيشو]

شكرا جزيلا لحضرتك ولكن الرجاء قراءة هذا الراى الذى صادفنى اثناءتصحفى بعض الواقع الاجنبية
(name of the English language) or an adjective (born in England). However, as spoken, the ambiguity disappears, because the speaker has to choose between realizing English + teacher as a compound, with main stress on English,secondary stress on teacher, and the interpretation teacher of English, or as an [adjective + noun] phrase, with reduced stress on English, full stress on teacher, and the interpretation England-born teacher (or maybe UK-born teacher, I'm not sure).
وايضا
means "person who teaches one or more of the various topics that are considered English," and that includes literature, grammar, writing, etc. This meaning is so ingrained that if we wanted to indicate that we had a teacher who is from England, we'd have to explain it by saying something along the lines of "my teacher is from England" or "my teacher is English."

[الاستاذ خالد زلط]

Sorry, there is no differentiation of meaning by stress in that way.
"Scottish teachers are conservative, but English teachers are more liberal." Stress relates to ethnicity, not subject taught.
"Physics teachers are conservative, but English teachers are more liberal." Stress relates to subject taught, not ethnicity.
In normal conversation I would expect no difference whatsoever in the enunciation of "English teacher" as meaning ethnic English teacher and teacher of English. Those meanings depend on context, not on stress.
جزاك الله خيرا يا مستر علي افادتنا.