What Is CLDR? Common Locale Data Repository, Explained

CLDR (Common Locale Data Repository) is the shared database that tells software how each locale formats dates, numbers, currencies, and plurals. The Unicode Consortium maintains it, and it's the reference most programming languages and frameworks quietly rely on.

The reason it exists: 'the right format' is different everywhere, and no team should rediscover it locale by locale. CLDR records that 1,000.50 in the United States is 1.000,50 in Spain, that the week starts on Monday in one place and Sunday in another, that currency symbols sit before the amount here and after it there, and that plural rules vary (English has two forms, Arabic has six). It covers hundreds of locales and is updated twice a year. Sorting belongs to it too: CLDR knows that ñ files after n in Spanish and that Swedish places å, ä, and ö at the end of the alphabet.

Developers almost never edit this data by hand. They reach it through libraries, the ICU project, the browser's Intl API, or a framework's formatting functions, all of which read from CLDR underneath. That's what makes a date render as '20 July 2026' for one user and '20 de julio de 2026' for another with no custom code.

Using CLDR-backed formatting is a core part of internationalization: it's how a product handles locale differences correctly without a developer guessing at them.

Why it matters for custom software

The multilingual-ready software we build formats dates, numbers, and currencies through CLDR-backed libraries rather than hard-coded rules. A new market inherits correct local formatting for free, which is one less thing to fix when a client expands into another language.