Where does “Rusça” come from?

Rusça (Turkish) comes from Turkish -çe, from Ottoman Turkish -ce, from Proto-Turkic *-če.

Ancestry of “Rusça”, step by step

Step	Language	Word	Meaning
1	Turkish	-çe	like, -like, -ly; -ish; as if, as though; in the...
2	Ottoman Turkish	-ce	—
3	Proto-Turkic	*-če	—