Restrained, after the language used left them speechless (6-4)
I believe the answer is:
tongue-tied
'speechless' is the definition.
(thesaurus)
'restrained after the language' is the wordplay.
'restrained' becomes 'tied' (tying is a kind of restraining).
'after' means one lot of letters go next to another.
'the language' becomes 'tongue' (tongue can mean a language).
'tied' put after 'tongue' is 'TONGUE-TIED'.
'used left them' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for tongue-tied that I've seen before include "Speechless with shyness" , "(Out of shyness) barely able to speak" , "Unable to say" , "Unable to speak coherently" , "Speechless from embarrassment" .)