To be honest, I can't see that English teachers have any greater challenges that teachers have in any other language. If anything, due to the widespread use of English around the world, I would have assumed teaching English would have been slightly easier.
Students can see the tangible benefits of learning a 'global' language, and teachers have a greater pool of resources from which to find teaching material.
On the other hand, there are always challenges to teaching any language - especially if you are teaching it as a second language.
Having studied "Romance" languages like French and Italian, I'd say that English grammar is slightly less structured - in that there are more exceptions and unusual conjugations, verbs that don't obey the rules... And I can imagine that makes English a tricky language to teach.
