Guild Wars 2

I have a level 80 guardian that I barely use. If I delete it and make a new one later (or immediately, whatever), would the new character retain the traits or do I have to unlock them again?

You’d have to unlock them again.

Chars made before the change to traits will have the old system, even if you never leveled them and they’ve been sitting at level one all this time. Any char made after the new trait system was put in will progress under its rules, buying or doing the events to get the traits.