Goblin translated old lines (5)
I believe the answer is:
troll
'goblin' is the definition.
(I've seen this before)
'translated old lines' is the wordplay.
'translated' becomes 'tr' (abbreviation used when referencing books).
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'lines' becomes 'll' (I've seen this in other clues).
'tr'+'o'+'ll'='TROLL'
(Other definitions for troll that I've seen before include "online commenter" , "Supernatural cave-dweller" , "Supernatural creature of Scandinavian folklore" , "Provocative poster" , "Ugly creature of folklore" .)