It might not be the most practical solution, but you could include a Helm of Comprehending Languages in the chest. This allows the wearer to cast Comprehend Languages at will.
For the duration, you understand the literal meaning of any spoken language that you hear. You also understand any written language that you see, but you must be touching the surface on which the words are written
A cheaper/smaller/lighter alternative would be to include a scroll of Comprehend Languages, but that would assume the receiver is or has access to a spellcaster that can use it.
Scrolls are written in a "mystical cipher" that anyone can read so long as the spell is on their list.