Source: Dungeon Master's Guide

Weapon (Dagger, Rapier, Scimitar, Shortsword, Sickle, or Spear), Common (Requires Attunement)

While this weapon is on your person, you understand the nonwritten communication of all Fey, and they understand yours.

Secret Message. As a Magic action, you can use the weapon to cast Message. Once this property is used, it can’t be used again until the next dawn.