can I make a localization mod on the vanilla maps(changing the weapons,names).

Well, you might be able to replace the entire stock core.lvl? It won't be an easy thing to do, you'd have to do some pretty complicated file editing (someone please correct me if I'm mistaken)

how, which files?

The core.lvl file in your gamedata/lvl_pc folder. I would not try it though, it could mess some stuff up.

I just looked in my back up core.lvl with hex edit, but I could not find anything.