You may speak no language other than English, but even so you are probably more multilingual than you think. That thought came to me as I read A Certain "Je Ne Sais Quoi" by Chloe Rhodes. The 175-page book contains scores of words and phrases from other languages that English speakers know and, in many cases, use on a regular basis.
We probably know such Latin phrases as bona fide, ex libris, et cetera, carpe diem, ad hoc, ipso facto, in loco parentis, in camera, habeas corpus, modus operandi, quid pro quo, status quo and vice versa.
If you ever say a la carte, deja vu, esprit de corps, en masse, faux pas, fait accompli, femme fatale, menage a trois, tour de force, savoir faire, nom de plume or haute cuisine, then you speak at least a smattering of French.
You probably also know a little Greek (ho polloi), Mandarin (feng shui and gung ho), Yiddish (klutz and kosher), German (wanderlust and wunderkind), Hawaiian (kahuna) and several other languages. Of course, most of these words and phrases have been used by English speakers for so long that they not only seem English but, in fact, are English. The English language regularly swallows up useful vocabulary from other languages and makes it its own.
One must be careful when trying to use these foreign words and phrases in foreign countries, however. As Rhodes explains, many of them are pronounced quite differently in the original languages, and many of them mean something quite different from what they have come to mean in English. In the United States a la mode (or more commonly alamode) means "with ice cream." In France it means "fashionable." The phrase c'est la vie (that's life) is now considered old-fashioned in France, so it's probably best to avoid it. If you say coup de grace the way most Americans say it, by leaving out the final "s" sound, it means "neck of fat" in France. The phrase double entendre, so popular in the United States, is considered obsolete in France, where they prefer double sens or double entente to mean the same thing.
One of the oddest things in the book has to do with the phrase art nouveau, a popular term in the U.S. to refer to new art. In France, however, Rhodes says they use an English phrase "modern style" to mean the same thing.