Much more useful than Americans tend to assume. Knowledge of at least one foreign language should be mandatory for every college grad. It's not just a matter of being able to communicate in another language; it's also essential to clear thinking. Very useful in the wider world as well. English may be the international language, but foreigners still think and (most of the time) speak in their native languages; if you don't understand their language, it's extremely difficult to really understand them or their country.
