Notification emails are not translated

[Alanaktion]

The notifications should use the user's language setting, followed by the global language setting to select translations for notification email components.

[Alanaktion]

Notification email language currently matches the sender's language, not the recipient's. We need to cleanly change the app language to match the user's preference when it's set. This isn't perfect, as many users will be using an English-language site, but let their browser determine the display language automatically when browsing, which we don't keep track of when that user isn't present. The best we can do with the current data is send emails following the user's manual setting if there is one, and hope the default on the site works if it's not set.