Of course there is not one “English Language” to be taught. What you teach will depend very much on the make-up of your students, for example what their level is and the reason they are studying English.
The following classes are going to learn very different kinds of English:
- students heading off to the USA to study law at university there
- a French business delegation wanting to deal with Chinese factory owners
- a Spanish footballer going to play for a club in the UK
- toddlers at nursery school
- Afghani immigrants just arrived in Australia
- a class of teenagers taking English at school for an exam
Within ELT there is also the variety of English to be considered.
and so on. In fact, there is never a single ‘English’ to be taught but just a subset of the language.