What is CLDR (Common Locale Data Repository)?

CLDR, the Common Locale Data Repository, is a dataset maintained by the Unicode Consortium that describes locale conventions for the world's languages: plural rules, date and time patterns, number and currency formats, sort orders, and translated names for languages, regions, and time zones. The data is compiled from contributions by native speakers and member organizations, and it is released on a regular cadence.

Its importance is that almost everything consumes it. The ICU library ships CLDR data, and through ICU it reaches operating systems, browsers, databases, and language runtimes. When PHP's intl extension formats a date for de_DE or picks the right plural category for Polish, the answer ultimately comes from CLDR.

For developers, the practical takeaway is: do not hand-roll locale conventions. If you find yourself writing a switch statement over language codes to decide decimal separators or plural forms, there is CLDR-backed machinery (NumberFormatter, MessageFormatter, IntlDateFormatter) that already knows the answer and gets updated as conventions evolve.