I googled this. Seemed the whole thing was translated in 2008 (I guess when the comic was first published.
Graft = grind, hard work
Chocca = short for ‘chockablock’ meaning filled up as far as it will go, packed to the gunwhales, loaded, full up
firtle = various meanings for this, some of them extremely rude, but used here in the sense of ‘mess about’, as in the Scottish word, ‘futer’
mithered = nagged at, bothered, whinged at
mental = mental
and that = ‘and all that’, etc., English equivalent of ‘n stuff’.
Monster trucks = large amounts, and slightly bizarre with it.