title: mark lables for translation in Django Forms
body: <p>Let's say I have this form: </p>
  
  <pre><code>class RSVPForm(forms.Form):
    attending_dinner= forms.ChoiceField(_('attending_dinner'), choices=VISIBLE_ATTENDING_CHOICES, initial='yes', widget=forms.RadioSelect)
    attending_brunch = forms.ChoiceField(choices=VISIBLE_ATTENDING_CHOICES, initial='yes', widget=forms.RadioSelect)
    number_of_guests = forms.IntegerField(initial=0)
  </code></pre>
  
  <p>How can I mark the fields' names ex. attending_dinner for translation ?</p>