My husband, when he was a teen in Japan in the 1950s, was taught French by a native Spanish speaker I think multiple languages would come in handy teaching English or one of the other languages in another country to English-speakers or non.

Or, you could be a corporate spy My girlfriend knew French and German and worked in the pastry/chocolate businesses and her clients did not know she spoke those languages so would talk in their native language, thinking they were "safe".