No experience here, as I am the typical American tourist (actually, one thing that has held me back from overseas trips, aside from money, has been that I don't know a foreign language well enough for where I would want to visit, and I don't want to -be- the "typical American tourist").
With that said, though, I think the idea of teaching in a native language engineering and other skills is likely the best way to do things, but that you would need to have a good grounding in English (and how to express those same concepts in English) as well, simply because it (English) is the "lingua franca" of the world (for just about everything, it seems - not just scientific or engineering pursuits).
Which kinds puts lie to my first statement - since English is the "lingua franca" of the world (much like latin used to be), and doesn't seem to be dying out any time soon (though speculating on what might replace it could be an interesting discussion), why should I worry about a foreign language in order to travel? My own personal though on this, though not germane to this discussion, is that I don't want to appear rude and ignorant; our American society constantly crows about how foreign visitors and immigrants should "speak english", but rarely do people from here care about the opposite (doing as the romans do, and all that, I suppose). I am in the camp that says if I am travelling to a foreign country, it would be hypocritical of me to expect everyone to speak english.
I wonder if that puts me in a minority of Americans, in some fashion...?