 ICU User Guide by the Unicode Consortium

Official project primary documentation. Introduction to ICU: C/C++ and Java libraries and internationalization services. Linked sections Normalization, Formatting Numbers, Formatting Messages, Locales and Resources document text equivalence and locale-sensitive services. No current release number or unnamed personal authors inferred.

Locale chapter: Overview, The Locale Concept, Default Locales, and Locales and Services; locale identifiers, service-dependent behavior and fallback.