Origin of mangled German saying (5)
I believe the answer is:
motto
'saying' is the definition.
(I know that motto is a type of saying)
'origin of mangled german' is the wordplay.
'origin of' suggests taking the first letters.
'german' becomes 'otto' (common German name).
The first letter of 'mangled' is 'm'.
'm'+'otto'='MOTTO'
(Other definitions for motto that I've seen before include "Phrase in a Christmas cracker" , "Christmas cracker text" , "Catchcry, slogan" , "Words often found on coat of arms" , "Slogan encapsulating self-image" .)