Current line in article from Frankfurt? One’s not seriously engaged (5)
I believe the answer is:
idler
'one's not seriously engaged' is the definition.
I can't judge whether this definition defines the answer.
'current line in article from frankfurt?' is the subsidiary indication.
'current' becomes 'i' (symbol for electric current).
'line' becomes 'l'.
'in' is an insertion indicator.
'article from frankfurt?' becomes 'der' (article in German).
'l' placed into 'der' is 'dler'.
'i'+'dler'='idler'
(Other definitions for idler that I've seen before include "Man off watch" , "Layabout; ship crewman not on watch" , "One reluctant to work" , "Someone unemployed" , "One who doesn't want to work" .)