Liberal German certainly not upset to be featured in warrant (7)
I believe the answer is:
lenient
'liberal' is the definition.
(thesaurus)
'upset to be featured in warrant' is the wordplay.
'upset' shows that the letters should be reversed in order.
'to' becomes 'nein' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'be featured in' indicates putting letters inside.
'warrant' becomes 'let' (I've seen this in another clue).
'nein' reversed gives 'nien'.
'nien' inserted inside 'let' is 'LENIENT'.
'german certainly not' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for lenient that I've seen before include "Easy, soft" , "Forbearing" , "Not severe in punishing" , "Mild and tolerant" , "Tolerant, rather than strict" .)