Checklist

• I have verified that that issue exists against the master branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to the discussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to be in the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

1. def model with unique_together attr

class Category(models.Model):
     name = models.CharField(max_length=20, verbose_name=_('name'))
     parent = models.ForeignKey('self', related_name='children', verbose_name=_('name'))
     class Meta:
           unique_together = ('name', 'parent',)

and create ModelViewSet for the model
2. create category(name='a', parent=1)
3. call create request with data (name='a', parent=1)

Expected behavior

Since I have set USE_I18N = True and USE_L10N = True, and added locale/xxx/django.po correctly.
I expect a error message well translated.

Actual behavior

fields with verbose_name are not translated.
As below

I've inspsected the DRF code, there are not any logic dealing with verbose_name in UniqueTogetherValidator.
Currently it just get field name of serializer field and return it to error_message of UniqueTogetherValidator.
As blow
https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/validators.py#L149

Is this by purpose or by mistake?
I can try to make a PR with test case and fix if it is needed.