Because English is so widely spoken, it has often been referred to as a "world language", the lingua franca of the modern era,[17] and while it is not an official language in most countries, it is currently the language most often taught as a foreign language.[18] It is, by international treaty, the official language for aeronautical[19] and maritime[20] communications. English is one of the official languages of the United Nations and many other international organizations, including the International Olympic Committee. It is also one of two co-official languages for astronauts (besides the Russian language) serving on board the International Space Station.