Language that’s a part of Klingon (5)
I believe the answer is:
lingo
'language' is the definition.
(informal term for language)
'part of klingon' is the wordplay.
'part of' says the answer is hidden in the clue.
'LINGO' is hidden in the letters of 'klingon'.
'that's a' is the link.
(Other definitions for lingo that I've seen before include "French?" , "Language (slang)" , "Unfamiliar language or jargon" , "Vernacular" , "Jargon, foreign language (informal)" .)