I found the link to the bug in the wiki and added it in the
comment.
I did some more tests with adult dwarves and weapons modded using gui/gm-editor (only minimum_size and two_handed are modified).
If the weapon's minimum_size is higher the the caste adult_size, dwarves will refuse to pickup their equipment.
If equipped without a shield, dwarves with a size_base (not size_cur) below the weapon's two_handed value will use multigrasp, others will use only one hand.
If a shield is added in the uniform, all dwarves are able to wield the weapon in a single hand.
This is from looking at dwarves during their "Individual Combat Drill" not actual combat.
two_handed looks more like a preference than a strict constraint or there is bug with the shield (or maybe they are able to equip it, but not really fight with it?).
Wiki says: Using any multi-grasp weapon in a single hand (i.e. with a shield in the other hand) gives you a disability to hit. Do not equip two-handed swords with a shield, for instance.
So equipping shield is not the right way to test. I need to give them only the weapon and check how they hold it. I'll make more test later to be sure I need to use size_base instead of size_cur.
Exact rules are:
- Can equip iff caste adult size ≥ weapon minimum_size (a weapon with minimum_size 6000 can be equipped by a dwarf)
- Can use in single hand iff dwarf size_base > weapon two_handed (a dwarf will use two hands if the weapon two_handed is equal to their size_base)