The term "to" and the term "to" are different in some languages.
Let me explain. "From 1:00 to 3:30" and "from Alice to Bob" look different e.g. in German.
"Von 1:00 bis 3:30" and "Von Alice an Bob".
In the messages interface "to" meaning "until" is displayed, where it should symbolize "addressed to". This leads to a weird and apparantly unprofessionally internationalised user experience.

I tend to insert a core string called "addressedto". It affects just messages/lib.php

FULL STEPS
Make sure you have a conversation in messages you will find by searching.
Open messages in german. ("Deutsch (de)").
By using "Search people and messages" ("Personen und Mitteilungen suchen") search and find your message in the results.

WHAT YOU EXPECTED
The columns representing the sender and the receiver are entiteled "Von" and "An"

WHAT ACTUALLY HAPPENS
The columns representing the sender and the receiver are entiteled "Von" and "Bis"

"Bis" having the meaning of "until".