international language; world language; global lingua franca
A language used for communication between people from different countries, such as English today.
英語は現代の国際語だ。
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
エスペラントは有名な国際語の一つです。
Esperanto is one of the well-known international auxiliary languages.
国際語 specifically means a language used for communication between different countries, while 共通語 more broadly covers any shared language, even within one country.
Compound of 国際 (international) + 語 (language).