x1=fP5 is a translation of translation x2=fP2=fZ5 from (intermediate) language x3=fP3=fZ4 to (final) language x4=fP4 by x5=fP1, with intermediate translation source x6=fZ2 from (starting) language x7=fZ3 by x8=fZ1.
fZ and fP indicate left and right fanva, respectively. Basically indicates a 'double' translation - a translation of a translation, which is what many translation engines do. See fanva. Graphically: x1 (lang. x4) <-x5- x6 (lang. x3) <-x8- x6 (lang. x7). Syn. terytraduki'yterytraduki, but shorter and more specific.