It says it counts as all types of weapons, probably so that any charname can use it, but what weapon focus/specialization and so on does it count as for feats? Or does feats not affect it at all?

It counts as a Longsword for Weapon Focus/Specialization purposes.

More info here: http://nwn2.wikia.com/wiki/Universal_sword

Thx. :)

Anyone know if you have to use the silver sword to finish the game? I was expecting that the pieces would be forged into a short sword, since my will -- supposedly -- was guiding it. Alas, no such luck.

You don't have to, but it would make the end game much harder.
But the swords power comes from the spells it can cast.
The +1 for having weapon focus in longswords is of little consequence.

Thing is, I'm a halfling rogue / fighter with massive dexterity, so I'll lose my shield, my dex bonus to hit, and the 4 feats invested in short sword.

Personally I think all that would be offset by the special features of the sword.
right click on the sword and examine it, and scroll through it's list of bonus's, aside from the spells it can cast.
But like I said, you don't have to use it.

There is a Mod which claims to do something like that. It lets you pick the kind of weapon of Gith you get:
https://neverwintervault.org/project/nwn2/hakpak/original-hakpak/silver-sword-fix

I have not tried this.

You can place weapon sets into your quick action bar so;
1 = short sword and shield until the bad guy is down then
2 = switch to the silver sword to finish him off

Thanks everyone! All is not lost. ;p