Localisation
Also said as L10n, Translation, Internationalisation, i18n
Adapting a game for other languages and places: translation, but also longer text, right-to-left reading, fonts, voice acting, date formats and culture. Internationalisation is the engineering that makes it possible.
Many players will never see your game in English. Retrofitting a game whose text is hard-coded and whose boxes fit only English is slow and expensive, and it shows.
Say it
“No text in code: everything goes in string tables from day one. Let every text box grow by at least 40% for German, and test the menus right to left before anyone builds more of them.”
Where you’ve seen it
The European Mega Drive release of Zero Wing in 1991 had the opening line "All your base are belong to us". It became one of the internet's first big jokes, and a lasting example of what a cheap translation looks like.
Not to be confused with translation
Translation changes the words. Localisation changes whatever else has to change as well, such as the jokes, the layouts and sometimes the content.