What term defines the language specific to a time period? [closed]

You use adjectives or adjective-like terms to modify the name of the language and this is meant to characterize the language as a whole. "Colloquial" is a term that has to do with the register of a language and "vernacular" has to do with the language spoken in a particular region or group (in particular if not the official language), so these terms have nothing to do with periods¹. There are a multitude of extant terms for the English spoken in various periods; here are a few.

• Mid-twentieth Century English, Middle English, Victorian English, Elizabethan English, Late Old English, Early 20th century English, Edwardian English, 1960's English, etc.

Here are two instances (provided by user Peter Shor) in which the language is not named but is instead identified generically; in fact, "vernacular" is the term used for that identification.

• 19th century vernacular, Southern vernacular

¹ _{What I mean to say when I write "has nothing to do with 'periods"' is that "vernacular" can't be used to specify a period, what provides the information proper to the period is the modifier.}