Mostly charge language group (5)
I believe the answer is:
indic
'language group' is the definition.
(large language group)
'mostly charge' is the wordplay.
'mostly' means to remove the last letter.
'charge' becomes 'indict' (indicting is a kind of charging).
'indict' with its last letter taken away is 'INDIC'.
(Other definitions for indic that I've seen before include "Group of languages including Sanskrit" , "Language" , "Like some tongues" .)