Foreign weapons, and weapons in general, are a bit odd currently. I'm not sure if the current model is just a placeholder for something much more complicated in the future, but I'd like to give you people my view on this so that maybe people using the search bar in the future could get ideas from it. This proposal is far less important than other things that Toady is and will be working on such as retiring fortresses, bugfixing, creating armies that can move outside your fortress and attack other settlements and so on, but I think it would expand a feature that's not particularly interesting at the moment. This could even be a fun mod, but I think this could be interesting for vanilla when the game is in its final stages of development many years from now. I think this would be classed as a "bloat" in the old terminology of features.
I suggest that foreign weapons be procedurally generated from a list like this:
http://en.wikipedia.org/wiki/List_of_premodern_combat_weapons, albeit without the weapons from 1400s+. Each civilisation in your world would have a number of exotic weapons in their possession adjustable through worldgen parameters. You could also create brand new weapons through artifacts, allowing the artifact maker to create the weapon repeatedly or even write it down in a book so his successors can learn the same. Perhaps books could be purchased from merchants containing various plans for fanciful new weapons. However, the total number of fanciful weapons in your world would be adjustable in worldgen, so if you want to keep things bare-bones (whips, daggers, short swords, long swords, war hammers, mauls, morningstars, bows, crossbows, blowguns, maces, battle axes, great axes etc) and simple as many of you probably would then you can still have that. It would be an optional thing, just like the number of types of titan/forgotten beast in your game.
It's up to Toady or you guys what weapons would actually be used in a list like that, because although there's a lot to be said for kataras and a wakizashi sword some of you may object somewhat to meeting a goblin carrying something like that. That said, maybe you could do away with some of the exotic names and make them more western european by calling things like the katara a "push dagger". There's also numerous types of sword that are almost exactly the same that you wouldn't really include, although you would make include something like a boomerang. I think there's more than enough perfectly unique weapons in there that you can use if you ignore the stuff that's almost exactly the same. Or, as an alternative, we have an overhaul that actually allows for things like the differences between a falchion and an arming sword to be taken into account. There was a sword in china called the dadao that was used from medieval times right up until WW2; it looked like a big, scary butcher's-knife-thing. It was popular because it could be used to great effect by people who weren't very skilled swordsmen, although a skilled swordsman with a more specialised blade would always be the better fighter. It would be nice if we could have that kind of thing in DF.
As things stand with the current version, there's not much difference between a falchion and a double-edged sword. I think though that could change when combat moves become better developed, so for example one could perhaps kill someone on the upstroke and downstroke. I hear in medieval times most people just used a single edged sword out of practicality but that's not to say that Dwarven legendary swordsmen couldn't find some crazy-ass use out of a sword like that.
There you have it, that's my proposal. I know other weapons have been suggested before but I think this may be a useful suggestion. I'd also like to finish by saying that Dwarven boomerang squads and Dwarven boomerang hunters would be the best thing in the universe. Concerned at the ammo consumption of your rangers when hunting various animals? No problem. Unfortunately though they'd probably have to use their own skill because if they used thrown then our adventurers would just power level with them.