The noun for the whole situation of several languages being used — by a person, a community, or a country. Where multilingual describes someone or something, multilingualism names the condition or the phenomenon itself: 'Multilingualism is normal in most of the world.' It is a discussion word. You meet it in education policy, research papers, government language plans, and newspaper opinion pieces — not in casual speech. Nobody tells a friend 'I love your multilingualism'; they say 'wow, you speak so many languages.' The word covers two rather different things, and writers often slide between them without saying which. One is individual multilingualism: one brain holding several languages. The other is societal multilingualism: a place where many languages are spoken, even if most residents speak only one of them. Taiwan is a good example of the second — Mandarin, Taiwanese, Hakka, and the Indigenous languages all live here, but few individuals speak them all. Because the word appears mostly in policy writing, it often carries an argument with it: people who use it are frequently defending the value of keeping languages alive rather than replacing them with one.

多語現象、多語主義（語言政策與教育研究的用詞）；指一個人或一個社會同時使用多種語言的狀態。