Platina stripped by old tongue (5)
I believe the answer is:
latin
'old tongue' is the definition.
(Latin is an ancient language)
'platina stripped' is the wordplay.
'stripped' indicates the central letters (outside letters removed).
The middle letters of 'platina' are 'LATIN'.
'by' is the link.
(Other definitions for latin that I've seen before include "difficult subject" , "The language of old Rome" , "'Dead language, though still taught (5)'" , "Parent language of French,Romanian" , "Language of ancient Rome" .)