What is "diglossia"?
Diglossia is when one community uses two different languages or dialects depending on the circumstances e.g. for written things and for casual conversation. A weird (not actual schoolbook) case of that is Swiss German. High German is used for written and formal things while Swiss German is used to speak.
Instruction: What is "diglossia"?
Context: 
Response: Diglossia is when one community uses two different languages or dialects depending on the circumstances e.g. for written things and for casual conversation. A weird (not actual schoolbook) case of that is Swiss German. High German is used for written and formal things while Swiss German is used to speak.