On Russian keyboard layout backslash (\) is in the same position as on US keyboards (electronically; the actual position may differ as the shape and arrangement of Enter, Shift and Backspace keys is not standardised here), the forward slash (/) is entered as Shift+\
As I understand, that layout was designed for MS-DOS by the group of computer enthusiasts that joint USA-USSR company Dialog gathered in 1990 by request of Microsoft during Bill Gates' first official visit to Moscow, and these enthusiasts were basically all programmers. Hence the layout they created is based on a US English for a convenience of keeping some punctuation marks in the same places. That makes it horrible for Russian typography, but such is life here.