The Greek that is translated as “convulsions” or similar in English is translated in Low German idiomatically with the reduplicative rüttel un schüttel for “shake” (translation by Johannes Jessen, publ. 1933, republ. 2006).
Following are a number of back-translations of Luke 9:39:
Nyongar: “An evil spirit quickly attacks him and screams and throws him down fitting so he foams at the mouth. The evil spirit always hurts him and will not leave him.” (Source: Warda-Kwabba Luke-Ang)
Uma: “When he is entered by an-evil-one, he shouts and thrashes-around, until his mouth foams. There is almost no going-out of the evil-one that makes-him-sick.” (Source: Uma Back Translation)
Yakan: “For he is demon possessed. Suddenly he will shout and then he becomes stiff and he convulses until his mouth is foaming. And the demon will only leave him when he is tired out (the child) and his body is bruised.” (Source: Yakan Back Translation)
Western Bukidnon Manobo: “Look at him because he is afflicted with a demon, and when it comes to afflict him, he suddenly screams and he shakes and he foams at the mouth, and this demon that afflicts him continues tormenting him until his body is bruised and the demon does not let go of him for a long time.” (Source: Western Bukidnon Manobo Back Translation)
Kankanaey: “Because there is a evil-spirit that possesses him. When it catches him, he suddenly-screams, convulses and his mouth foams. He excessively keeps-hardshipping him until he is exhausted and he doesn’t let-him-alone.” (Source: Kankanaey Back Translation)
Tagbanwa: “Every time he is made-crazy by an evil spirit, suddenly/unexpectedly he cries out, falls and stiffens, and his mouth froths. This one making him crazy really never leaves him and he’s been caused much pain.” (Source: Tagbanwa Back Translation)