A specialised archetype or template is only required to have one language in common with its flat precursor, enabling a flat output containing this language. This supports the common situation in which an international standard archetype with numerous translations is used as a basis for further specialisation in a particular country or project. Clearly, the latter has no need of, and quite probably no capability for including all the original translations in the specialisation.

However, if the specialised archetype language is not present at all in the parent flat, it will need to be added to the archetypes in the specialisation lineage first.

The languages present in the flat output will therefore be those languages available in both the flat parent (implying all previous archetypes / templates in the specialisation lineage) and the new specialisation. Any new languages introduced in the latter not available in the flat parent will be discarded.

Locale-specific overrides can be introduced for any linguistic element in an archetype, including the terminology. Such an override has a language code conforming to a subset of the IETF RFC 5646 language tag standard, namely the common 2-part language-region tag exemplified by 'en-GB' (British English), 'pt-BR' (Brazilian Portuguese), and so on. The tags are case-insensitive, but tools that create tags should follow the recommendation from the standard, which is that: