As I was testing another bug I came across this very interesting one - all of the languages except English are missing their respective translation throughout the site, and as a result, are in English.
I am unable at this time to compile a list of all of the missing translations, but to repro this:
1.) Select a non-English language in your Preferences > Interface
2.) Refresh the site.
3.) Open up your User Page and head to Preferences
4.) Notice multiple missing translations.
I have noticed that custom items, such as custom (non-default) fields, badges, and sections tend to have missing translations.