Dictionary.com Word FAQs
Should I use italics in foreign phrases in an English document?
It is certainly OK to use foreign phrases in your writing. If you are using a foreign expression that has not become common in English and it is likely to be unfamiliar to readers, then use italics. Example for using italics: He said "je ne sais pas." Example for leaving them out: "She discovered a ménage à trois." Other examples of commonly used foreign phrases that one should not italicize are: a priori, ciao, mea culpa, and merci. If a definition follows a foreign word or phrase, enclose the definition in parentheses, e.g., In his speech, he talked about defining cheveux (hair).