While compiling a dataset of presidential tidbits this Saturday evening I noticed that the foreign language skills have been deteriorating over time. In fact, we haven't elected a president with more than a passing knowledge of a foreign language since FDR. In contrast, our founding fathers were generally well-versed in at least Greek and Latin. James Madison, for example, was proficient in Greek, Latin, and Hebrew. Our greatest polyglot president to date is Thomas Jefferson, who in addition to Greek and Latin could speak French, Italian, and Spanish. Only one of our presidents, Martin van Buren, spoke a language natively besides English: he was raised in a Dutch-speaking community in New York and spoke Dutch at home. Disregarding Obama's limited knowledge of Indonesian, only one of our presidents has been able to speak a non-European / non-classical language: Herbert Hoover was proficient in Mandarin from his time living in China as a miner. His wife spoke the language, too.
I used data from Wikipedia.