What language would not be used in vernacular literature?

This question is quite ambiguous. The vernacular languages differ from country to county, and if you want to find out which languages would not be used, just take any languages that are official but not commonly spoken by the population. However, you must be careful not to count languages such as Belarusian as one of these, as it is not commonly spoken in Belarus, but, when spoken, is not used exclusively by the upper or ruling classes.