international language; world language; global lingua franca
A language used for communication between people from different countries, such as English today.
English is the international language of today.
constructed international auxiliary language
Specifically refers to planned languages like Esperanto, often contrasted with naturally evolved international languages.
See also: 国際補助語
Esperanto is one of the well-known international auxiliary languages.
Compound of 国際 (international) + 語 (language).