Unlike most flag carriers, fluency in the national language is not required, indeed 90% of CLX pilots can't speak a word of Luxembourgish (except maybe "moyen") Such a requirement would narrow the field somewhat.
I think we can assume from A 71s posts that the requirement for fluent English would have been an automatic fail point - certainly written and therefore probably spoken too!!!
As a native English speaker I am constantly impressed by my colleagues, of many different nationalities, firm grasp of technical and spoken English which puts my shaky attempts at French and Spanish to shame. Of course we Brits are renowned for our idleness in learning other languages - long live the Empire!