i18n Internationalization
Building software so that it can be adapted to other languages and regions — the abbreviation is i, 18 letters, n.
Distinct from localization (l10n), which is the translation work itself. i18n is the technical groundwork: no hardcoded strings, no sentence-building through concatenation, Unicode throughout, and layouts that survive German being 30% longer.
The traps are rarely the language itself. Plural rules vary (Polish has three forms), date and number formats are regional, collation order is language-dependent, and not every name splits into given and family name. ICU and CLDR exist precisely so you do not implement this yourself.