European mentioning completion (7)
I believe the answer is:
finnish
'european' is the definition.
(from Finland)
'mentioning completion' is the wordplay.
'mentioning' indicates a 'sounds like' (homophone) clue.
'completion' becomes 'finish' (finish is a kind of completion).
'finish' is a homophone of 'FINNISH'.
(Other definitions for finnish that I've seen before include "race" , "foreign language" , "Nationality of citizens of Helsinki" , "Eg, native to Helsinki" , "European language" .)