Jim Macklin wrote:
There have been a number of incidents and a few accidents
that were caused by or in which language was a factor. The
747s that collided on the runway at Tenerife was one of
those accidents. NASA safety reports cite many language
problems http://asrs.arc.nasa.gov/

The problem is compounded if English is not the native language of
either party. This was a factor in the Tenerife incident. It is bad
enough if only one side of the conversation is with a nonnative
English speaker.

Some years ago I was based at a busy Class C airport that seemed to
have a good number of visiting pilots with a limited command of English
(this was pre - 9/11).
Coming or going on a busy VFR weekend day was interesting, to say the
least.

David Johnson