I think it is an equivalent phenomena of being able to carry on drunken conversations with Glaswegians (or any thick accents etc) but later when sober the communication is broken and one might as well be in a non-English speaking country. In that case where you are in a foreign country the easy solution, as any English speaker knows, is to speak LOUDER. Eventually the natives will understand.)
Surely that is an illusion! Occasionally I have been convinced, when in my cups, that I am actually fluent in French, and the accommodating nods and smiles of those around me do little to persuade otherwise. I insist upon ordering in that language, and cover any lapses with what I am sure are the Frenchest of qu'est-ce que c'ests and qu'est-ce qu'on dits, delivered with a very Gallic wave of the hand. It is only with the morning that the awful truth dawns.