Where does “tnax-il” come from?

tnax-il (Maltese) comes from Maltese -il, from Arabic عَشَر — ten.

Ancestry of “tnax-il”, step by step

Step	Language	Word	Meaning
1	Maltese	-il	Used to form the attributive form of cardinal numbers 11 to 19
2	Arabic	عَشَر	ten