Diglossia
Diglossia is when a group of people have two languages or dialects that they use. One is the common language they use every day, and the other is either a much older version from centuries before (for example, Arabic or Chinese) or a similar but clearly different modern-day version (for example, Norwegian with Bokmål and Nynorsk).
Diglossia Media
The station board of Hapur Junction railway station in North India demonstrating digraphia of two formal registers, Hindi and Urdu, of a common vernacular, Hindustani, an example of triglossia.
