(Not a teacher)
I would say 'English teacher' as in 'a teacher of English' would be said with the maing stress on 'En-' and relatively equal stress on '-glish tea-cher'
I would say 'English teacher' as in 'a teacher who is English' would be said with the main stress on 'En-' and 'tea-', with '-glish and '-cher' being relatively unstressed.
The intonation is slightly different, but too complex for me to try and explain. Perhaps 'English teacher' - the teacher of English - is a more consistent intonation than 'English teacher' - the teach who is English - which is more varied.
In practice, I would say the biggest give-away would be context rather than stress or intonation.
- For Teachers