I found a bug during testing. If you have tried equipping the sword and failed, still have the knife, and equip a stick (or bone) if it's the last one, the option to switch weapons disappears, and the game will say that you're now barehanded and have to rely on your claws. The game will still use the weapon you chose though. The bug also appears when you enter battle and select the stick. I think this is caused because on line 540 of 'battle.rpy', you check if all of the weapons are == 0. However, you don't check for the knife, and the player might have something equipped already.
So basically there are 3 bugs:
1) You don't currently check for the knife on line 540 of 'battle.rpy'. This causes the game to show a message saying that the player has no weapons, even if they have a knife. ("现在的你赤手空拳，只能依靠自己的爪子了")
2) You again don't check for the knife on line 327 of 'battle.rpy', this stops the menu option to switch weapons from showing. ("选择武器")
3) You again don't check for the knife on lines 341, 361, 387 and 544.
4) These checks don't consider the currently equipped item either.
For a suggestion, I would move the 'Skill' button to it's own category. Basically it's currently like this:
>Choose weapon
>Battle
>>Skill
>>Attack
>Items
>Run
I'd change it to:
>Choose weapon
>Skill
>Attack
>Items
>Run