After forgetting English, Swiss girl adopts new language (5)
I believe the answer is:
hindi
'language' is the definition.
(Hindi is an example)
'after forgetting english swiss girl adopts new' is the wordplay.
'after forgetting' is a deletion indicator.
'english' becomes 'e' (abbreviation).
'swiss girl' becomes 'heidi' (fictional character in the Johanna Spyri novel).
'adopts' is an insertion indicator.
'new' becomes 'n'.
'heidi' with 'e' removed is 'hidi'.
'hidi' placed around 'n' is 'HINDI'.
(Other definitions for hindi that I've seen before include "Language derived from Sanskrit" , "Indian language" , "language many use" , "Asian language" , "One of India's official languages" .)