If you wanted to mod that in for yourself, that's very basic reaction stuff. Furry Fortress has wood, rock, bone and glass weapons. Very do-able. Gotta say though, having tried it, it's not super useful. Even relatively crappy metal weapons will outperform wood and stone, and any metal armor will render them useless. Outside of crazy dwarf tricks or crazy challenge games, there's not a lot of a point to it. It's a lot easier to put your resources into trade goods and obtain metal from a caravan.
Another interesting point is that the Dwarf Fortress materials engine doesn't actually reflect how flexible materials actually work(or as Putnam put it, non-isotropic) (i think). I think metal, rock and glass are relatively accurate, but wood, cloth, bone and flesh are vague approximations. Toady's lack of interest in wood is also made apparent by his idea that all woods have the exact same material properties, which is crazy inaccurate. Different woods are different, ratan and hickory are an easy example as far as impact, and a lot of new-world and tropical woods are super different from what grows natively in europe and asia, like hornbeam and ebony.
The thing with javelins is that Fortress Mode still doesn't have a way to mod in thrown weapons. The ability to mod in javelins, darts, boomerangs, hurlbats, shuriken, hunga mungas, etc, would be a super cool addition, but I fear any tampering with the combat system will be put off for a long long time.