Regret backing competition that includes a German, say (8)
I believe the answer is:
european
'german say' is the definition.
(german is a kind of European)
'regret backing competition that includes a' is the wordplay.
'regret' becomes 'rue' (to rue something is to regret it).
'backing' is a reversal indicator.
'competition' becomes 'open' (open is a kind of competition).
'that includes' means one lot of letters goes inside another.
'rue' back-to-front is 'eur'.
'open' enclosing 'a' is 'opean'.
'eur'+'opean'='EUROPEAN'
(Other definitions for european that I've seen before include "Inhabitant of the second smallest continent" , "The E of the EU" , "Continental is curiously A-one pure" , "Of a certain continent" , "Anti-UKIP" .)