Let me expand the problem.

Date class get "translator" variable in it constructor. "_" function 
assigned in constructor to "translator"'s gettext. Default value for 
"translator" is i18n from i18n.py module.

While creating Date instance the "translator" value left to default 
i18n class. Unfortunately, i18n class does not use trackers "language" 
setting and always stay in english.

Thus:
1. Real "translator" value does not pass to Date instance.
2. Default i18n instance have no relation to tracker "language" setting.

Other objects (not a Date) get real "translator" value from the tracker 
instance, i suspect.