Diachronic language
From Langmaker
A diachronic language is a language with an internal linguistic history. Such languages may be developed from a proto-language conlang, or may have descendent conlangs. It may also exist within a conlang family.
An important subcategory of diachronic languages are the so-called alternate history languages, or altlangs. The difference with other diachronic languages is that the latter are not developed from a constructed proto-language, but from a language that exists in the real world. Most numerous in this category are the romlangs, hypothetic offspring of Latin.
Diachronic languages are often embedded in a fictional world, or alternate history, in which the relationships between the languages are explained. In that case, we call them fictional diachronic languages.
