One's part is ruined by English language (9)
I believe the answer is:
esperanto
'language' is the definition.
(Esperanto is an example)
'one's part is ruined by english' is the wordplay.
'is ruined' is an anagram indicator.
'by' means one lot of letters go next to another.
'english' becomes 'e' (abbreviation).
'ones'+'part'='onespart'
'onespart' is an anagram of 'speranto'.
'speranto' after 'e' is 'ESPERANTO'.
(Other definitions for esperanto that I've seen before include "Parse note in the artificial language" , "in which many could communicate?" , "Ape tenors (anag.)" , "Universal language" , "Linguistic invention" .)