As interest in internationalisation and localisation grows, language and locale identification is needed for increasingly diverse situations. There is a growing consensus that existing standards for language identification are not fully meeting user needs and that more fully developed standards are needed. It is not always obvious how systems of identifiers should be extended to accommodate new usage scenarios, however.

This paper presents that view that part of the reason for this difficulty is a lack of an adequate ontological model for language and language-related categories. In existing practice, the two notions "language" and "locale" are assumed to cover the full range of distinctions to be made, whereas in fact there are other distinct language-related notions that may be at work and that may need to be reflected in systems of identification.

This paper proposes a set of notions for language-related categories that are relevant for information technologies (IT), and examines the relationships between them. It explores some usage scenarios and considers what ways of formulating identifiers might be appropriate for the various scenarios.