This sort of thing does not only occur in aviation.
Recently in the NT a dean at NTU received faxed death threats, death by decappitation, from several students, I think of Chinese origin.
The problem was basically that said students had paid for an English Standards test 'back home'. Having paid, they passed.
Then in Australia they paid for Uni tuition, expecting that they would pass, when in reality their understanding of the English language is such that they couldn't properly understand their lectures.
I would not be surprised if something similar occured with flying students too.