Luckily this problem never arose during my professional career. I was in a multi-lingual environment, and although English was our working language,there always seemed to be someone around with a knowledge of almost every European language plus a few outside the region.
There have been cases where even a knowledge of "technical" English is not enough, viz. the Mexican (?) who crashed in New York after running out of fuel, but not making it clear to ATC; and the case where the last words on the CVR, after a terrain warning, were, "Shut up, gringo."