How does one define an "appropriate" grasp of the English language? While living abroad, I traveled around Asia with a non-native English speaker. Because her English was better than my Chinese, we went on the English tours at the locations we were at. Her English was good, but when the tour guide was not a native English speaker, she had a very hard time understanding the guide, even though I had no problem.

Since in many cases English is considered one of the international languages for airline announcements, I would hope that it would be as clear as possible, esp for those who are listening in English as a second language.