How to bury cable with the intention of adding lighting?
In my opinion the best thing to do with "intention of future..." is empty conduit. Under NEC rules, 18" deep unless protected by various means (such as a concrete path on top) which alter the required burial depth. Your local rules may vary, since I also don't recognize "NYY" as a cable type I'm familiar with in North America.

Buried cable is making a bet that you guessed right. Conduit lets you guess right about where it goes, without concern about the actual wiring until you get to that point, and you can change it out later if need be, without having to dig the trench again.

I like to add at least one more conduit than I know what I'm using them for - conduit is cheap, trenches are expensive.