Where does “falskr” come from?

falskr (Old Norse) comes from Middle Low German valsch, from Finnish falski, from Swedish falsk — false; untrustworthy.

Ancestry of “falskr”, step by step

Step	Language	Word	Meaning
1	Middle Low German	valsch	false, wrong; falsely, wrongly; fraud, trickery
2	Finnish	falski	fake, insincere, phony; false, spurious; out of...
3	Swedish	falsk	false; untrustworthy

falskr — Etymology, Origin & Word History | Etymology Explorer