Let's suppose that you have the Idea model, with a foreign key pointing to the Category model.

1. Let's define the Category model in the categories app, as follows:

# myproject/apps/categories/models.py
from django.db import models
from django.utils.translation import gettext_lazy as _

from myproject.apps.core.model_fields import MultilingualCharField


class Category(models.Model):
    title = MultilingualCharField(
        _("Title"),
        max_length=200,
    )

    class Meta:
        verbose_name = _("Category")
        verbose_name_plural = _("Categories")

    def __str__(self):
        return self.title

2. Let's define the Idea model in the ideas app, as follows:

# myproject/apps/ideas/models.py
from django.db import models
from django.conf import settings
from django.utils.translation import gettext_lazy as _

from myproject.apps.core.model_fields import (
    MultilingualCharField,
    MultilingualTextField,
)

class Idea(models.Model):
    title = MultilingualCharField(
        _("Title"),
        max_length=200,
    )
    content = MultilingualTextField(
        _("Content"),
    )
    category = models.ForeignKey(
        "categories.Category",
        verbose_name=_("Category"),
        blank=True,
        null=True,
        on_delete=models.SET_NULL,
        related_name="category_ideas",
    )

    class Meta:
        verbose_name = _("Idea")
        verbose_name_plural = _("Ideas")

    def __str__(self):
        return self.title

3. Create and execute initial migrations by using the following commands:

(env)$ python manage.py makemigrations categories
(env)$ python manage.py makemigrations ideas
(env)$ python manage.py migrate