French

French was a Latin language which originated in northern France. It was spoken natively by millions around the world and was an official language of numerous countries, including France, Belgium, and Canada.

History
English Quidditch terminology was uniformly used throughout Europe for many centuries. In 1635, the Académie française des sorciers was founded, and created French equivalents for these terms.

An advertisement for a magic translator's services that appeared in the classified section of an issue of the Quibbler listed several languages available for translation, including Chinese, "Eastern European" (presumably Russian or another language in the Slavic family), Japanese, and the Latin Languages (which presumably included French).