i18n: Episode Errors are stored as user displayed strings

Changing the language on the device will retain the message in the previous language.

1. Set the device to a specific language
2. Generate an episode error by taking the device offline and then attempting to play an episode that hasn't been downloaded.
3. Switch to a new language
4. Notice that the error is still in the previous language.

Reproduce the issue by following the listed offline playback and language-switch steps, then trace where the episode error is created and stored in the iOS app. Done means the error is shown in the newly selected language after switching languages.

Written by the indexing model from the issue text.