Fix support for Indonesian language

Admittedly, the problem was identified by the new system checks framework (after removing ``models = None`` is ``modeltranslation.tests``, more on this later), however the messages were a bit cryptic (*), so I've added a simple specific test.

Note that the Indonesian language is now in the [default ``LANGUAGES``](https://github.com/django/django/blob/master/django/conf/global_settings.py#L88), so it's not so unlikely that non-Indonesians run into the problem.

(*) ``ForeignKeyModel.test_id: (models.E006) The field 'test_id' clashes with the field 'test' from model 'foreignkeymodel'``