A few of the weapons you mentioned are already in the game under different names. Some of the weapons you mentioned also don’t need to both be implemented. Claymores and bastard swords could really just be added in as one large sword. Dirks are knives, which are already in game. Military picks and halberds are also in game, I think. Rapiers wouldn’t fit in the game in my opinion, because they really didn’t see a rise in use until the 1500-1600s. They were better with the use of less armor and Battle Brothers is meant to be a gritty, medieval-style world. The ‘celtic sword’ and ‘viking sword’ you mentioned are confusing me, though. Both cultures had multiple styles for their swords, so which do you mean? Also, the game is supposed to have certain elements based off of real-world cultures, but without using the proper names because, after all, it is in a fantasy world. So really the viking and celtic swords could just be broadswords or shortswords.
I do like your helmet ideas and a few of those weapons.
Sorry to burst your bubble, but a bastard sword aka hand and a half sword, is only slightly bigger than a long sword, and can be wielded with one or two hands. A claymore is a much larger weapon, and cannot be wielded with one hand. A perfect example is William Wallace using one in braveheart. There are no military picks or halberds in the game thus far, unless they are an “named” weapon I haven’t found yet. You must be mistaking an ordinary miners pick and a billhook, for a military pick and a halberd. You should really know what you talking about before posting something as fact. Yes some of the weapons listed in the OP are similar to weapons already in the game, however the “named” items have a unique names. So for example, a named dagger could be called “Venomous Dirk” Or an ordinary padded leather armor could be called “Studded Hide”
A wise general wins before the battle, while the ignorant general must fight to win - Zhuge Liang