How to translate field label automatically when using flask-admin?

I would like to know how to use Flask-BabelEx(which is recommended by Flask-Admin) to translate field labels automatically when it's been generated by flask-admin.

For example, If I have a field which is defined as below:

class PurchaseOrder(Base):
    __tablename__ = 'purchase_order'
    id = Column(Integer, primary_key=True)
    logistic_amount = Column(Numeric(xxxx))

    def __unicode__(self):
        return self.id

And the view is defiend as

class PurchaseOrderAdmin(ModelView):
    column_labels = dict(logistic_amount=gettext("logistic_amount"),)

Then register to the admin as below:

    admin.add_view(PurchaseOrderAdmin(PurchaseOrder, db_session, category='Order'))

Here is how I init babel:

babel = Babel(app, default_locale="zh_CN", default_timezone="CST")

@babel.localeselector
def get_locale():
    override = request.args.get('lang')
    if override:
        session['lang'] = override
    return session.get('lang', 'zh_CN')

And I have generated the follow files:

translations/zh_CN/LC_MESSAGES/messages.mo
translations/zh_CN/LC_MESSAGES/messages.po

Content of file messages.po shown below:

msgid ""
msgstr ""
msgid "logistic_amount"
msgstr "物流费用"

But seems the key(logistic_amount) rather than the translated string(物流费用) is displaying in the list and edit page all the time.

Is there any piece missing here?

Thanks for the help.

Solution

We need to use lazy_gettext rather than gettext to make it work, examples as below:

adminViews.add_view(SalesOrderAdmin(SalesOrder, db_session, name=lazy_gettext("Sales Order")))

And

class PurchaseOrderAdmin(ModelView):
    column_labels = dict(logistic_amount=lazy_gettext("logistic_amount"),)