The Bug:

The error message "Invalid session id", which is shown after the player unsuccessfully tries to join a Realm server, is untranslatable.

Below I have attached an image which shows the message being displayed in English despite me having Swedish as the selected language.

Observed Behavior:

The Realms error message "Invalid session id" is untranslatable.

Expected Behavior:

The Realms error message "Invalid session id" is translatable with a string on Crowdin.