It also helped that his accidental cover story was as a resident of a Klatchian town whose residents were a byword for stupidity: the locals believed him to be from Ur also the name of a real city of ancient Mesopotamia because that's what he said when they asked him.
He always dines at the Y.
Michael is clearly panicking for a second before offering to switch to English instead.
Of course, they generally use their skill in deciphering texts, not actually speaking it.
Interestingly, his French is said to be poor in these books until he overwinters in a French household, but stories set earlier in his career have him quite fluent and establish that he learned it from an expatriate tutor as a boy—evidently as his service took him hither and thither, his French skills rusted and his Spanish learned later during a two-year spell as a prisoner of war improved.
Whereas most Cunning Linguists go from mild-mannered to badass, he does it the other way around.