Where does “lambatkan” come from?

lambatkan (Indonesian) comes from Indonesian -kan, from Malay -kan, from Proto-Malayic *-kən.

Ancestry of “lambatkan”, step by step

Step	Language	Word	Meaning
1	Indonesian	-kan	Used to indicate transitive imperative verbs;...
2	Malay	-kan	Used to indicate transitive imperative verbs;...
3	Proto-Malayic	*-kən	—