literate percent - indicates the percentage of the country's population that is literate, based on literacy information from the World Bank, CIA Factbook, and others.
language population - the number of people fluent in that language in that country, including both first and second language speakers. The level of fluency is that necessary to use a UI on a computer, smartphone, or similar devices. Reliable information is difficult to obtain; the information in CLDR is an estimate culled from different sources.
writing percent (writingPercent) - percentage of the population fluent in that language in that country who regularly read or write a significant amount in that language. Ideally, the regularity would be measured as "7-day actives". Reliable information is difficult to obtain; the information in CLDR is a best estimate culled from different sources.
customary modern usage - The terms or characters commonly used in modern contexts: newspapers, journals, lay publications, street signs, commercial signage, common geographic names, company names, and so on. It does not include terms or characters that are only commonly used in technical or academic contexts such as mathematical expressions, archaic or historic texts, citations of archaic words, liturgical texts, or pedagogical use.
official language - as used in CLDR, a language that can generally be used in communications with a central government. That is, people can expect that essentially all communication from the government is available in that language (ballots, information pamphlets, legal documents, …) and that they can use that language in communicating to the central government (petitions, forms, …).
Official languages for a country are not necessarily the same as those with official legal status in the country. For example, Irish is declared to be an official language in Ireland, but English has no such formal status in the United States. Languages such as the latter are called de facto official languages. As another example, German has legal status in Italy, but cannot be used in all communications with the central government, and is thus not an official language of Italy for CLDR purposes. Such languages are official regional or official minority languages.
official regional language - a language that is official (de jure or de facto) in a major region within a country, but does not qualify as an official language of the country as a whole. For example, it can be used in an official petition to a provincial government, but not the central government. The term "major" is meant to distinguish from smaller-scale usage, such as for a town or village.
official minority language - a language that has some official governmental status, but is not an official language of the country or of a substantial region.