Importance of English
Thorny,
When you arrive at the airlines and are flying international routes, you will understand the absolute necessity of a common aviation language. Situational awareness, especially in the airport traffic area, is greatly reduced when the pilots are not speaking the same language. Improper communications will kill people just as fast, if not faster, than poor piloting skills.
As far as a shortage of Instructors goes. Only the largest flight schools in the US are suffering a shortage. Most pilots are not willing to move across the country for an instructing job. It just doesn't make economic sense. So when a large school taps out the local market, it is hard for them to find instructors. Instructors don't generate huge income for a flight school so it is usually not worth their while to pay immigration costs.
Good luck!