一刀两断的英语:make a clean break with; break off all relations with; break with ... once for all; cut in two with one stroke of the knife; cut the (gordian) knot; sever with [at] one blow [one stroke]
一刀两断的法语:trancher en deux d'un coup de couteau;trancher résolument;couper(rompre)les ponts;cesser toutes relations avec qn