Currently all emails are going out with the locale of en-us.

While there is a language preference control in the user account area, that preference only persists for the duration of a user's web session. Apparently, this has always been the way in which this preference control operated. The pre-SUL version of the site leveraged a user's home wiki as a proxy for their locale, as the locale for a user was mapped to their home wiki. This would have been correct often, but not always. When we moved to SUL, we also moved to setting the default for a session to the locale requested by a user's browser, because that's how the web should work.

But: emails are not typically fired off from within the web session of the recipient. Because of that, emails are getting generated with the system locale, which is en-us. We need to persistently store each users' preferred language, and apply that preference to emails sent to them.

We should probably have two states:

1. the user hasn't actually used the preference control. In this case, we should default the setting to their browser's locale. The ui should make it clear that this is an overridable default. In this case emails will go out using whatever locale the user had set when they last visited.
2. the user went out of their way to make a choice. In this case we should always respect that choice. This should always override the detected locale, but it should allow the user to clear out the selected value and return to auto-defaulting.