I suggest drawing inspiration from Magic the Gathering's reminder text. The cards' text has to be written in precise legalese so that it technically functions under the rules, but that can be hard to parse. The solution are italicized sentences between parentheses that explain what's going on in plainer english.
"When you are wielding a melee weapon in one hand and no other weapons (versatile weapons are wielded with two hands if one is empty)".
Something like that.
