 Common Locale Data & Rules

CLDR, currently expanded as Common Locale Data & Rules, is the Unicode project supplying structured data and rules for locale-sensitive software. It supports conventions such as date, number and unit formatting. The older name Common Locale Data Repository identifies the same project.^[ref]

A locale identifies the language-related and regional conventions relevant to a software operation. Representing a character and choosing how to format a date are different tasks: Unicode character properties alone do not specify every cultural convention. CLDR combines curated data with a specification of structures and algorithms, plus code for collecting and processing those data.^[ref]

An original ambiguity example uses the string 03/04/2026. Under a day/month/year pattern it represents3April; under a month/day/year pattern it represents4March. The identical stored code points permit both readings until a format convention is specified. The example illustrates missing contextual information; it is not a quotation of the default format for a particular named locale.

Now imagine a program that stores a date as separate year, month and day values and formats it only for presentation. Keeping the represented value distinct from its localized string allows two users to see different forms of the same date. Parsing a user-facing string in turn requires the intended conventions, rather than assuming that visible punctuation supplies them unambiguously.

Applications often consume CLDR through libraries such as International Components for Unicode. Recording the relevant data version and formatting options makes an output example reproducible: a library name alone does not specify every rule or data revision used.^[ref]