Nothing is shown by glib sort of language (6)
I believe the answer is:
patois
'sort of language' is the definition.
'nothing is shown by glib' is the wordplay.
'nothing' becomes 'o' (looks like zero - 0).
'shown by' says to put letters next to each other.
'glib' becomes 'pat' ('pat' can be a synonym of 'glib').
'o'+'is'='ois'
'ois' put after 'pat' is 'PATOIS'.
(Other definitions for patois that I've seen before include "Local dialect heard in patios" , "manner of speaking" , "Kind of dialect, from French" , "Dialect, vernacular" , "Spoken regional dialect" .)