Types of individual languages
In the code table for ISO 639-3, the individual languages are identified as being of one of the following five types.
Living languages
A language is listed as living when there are people still living who learned it as a first language. This part of ISO 639 also includes identifiers for languages that are no longer living.
Extinct languages
A language is listed as extinct if it has gone extinct in recent times. (e.g. in the last few centuries). The criteria for identifying distinct languages in these case are based on intelligibility (as defined for individual languages).
Historic languages
A language is listed as historic when it is considered to be distinct from any modern languages that are descended from it: for instance, Old English and Middle English. In these cases, the language did not become extinct; rather, it changed into a different language over time. Here, too, the criterion is that the language have a literature that is treated distinctly by the scholarly community.
Constructed languages
This part of ISO 639 also includes identifiers that denote constructed (or artificial) languages. In order to qualify for inclusion the language must have a literature and it must be designed for the purpose of human communication. It must be a complete language, and be in use for human communication by some community long enough to be passed to a second generation of users. Specifically excluded are reconstructed languages and computer programming languages.