old_contents: from django.db import models
  from django.core.exceptions import ValidationError
  from django.template import TemplateDoesNotExist
  from django.utils.translation import ugettext_lazy as _
  from django.template.loader import get_template
  
  
  def validate_template_path(name):
      try:
          get_template(name, using="tex")
      except TemplateDoesNotExist:
          raise ValidationError(_("Template not found."))
  
  
  class TeXTemplateFile(models.Model):
      title = models.CharField(max_length=255)
      name = models.CharField(max_length=255, validators=[validate_template_path])
  
      class Meta:
          abstract = True
  
new_contents: from django.db import models
  from django.core.exceptions import ValidationError
  from django.template import TemplateDoesNotExist
  from django.utils.translation import gettext_lazy as _
  from django.template.loader import get_template
  
  
  def validate_template_path(name):
      try:
          get_template(name, using="tex")
      except TemplateDoesNotExist:
          raise ValidationError(_("Template not found."))
  
  
  class TeXTemplateFile(models.Model):
      title = models.CharField(max_length=255)
      name = models.CharField(max_length=255, validators=[validate_template_path])
  
      class Meta:
          abstract = True
  
subject: Replace ugettext_laxy