How to change the date field value correctly?

Question

Django

There is a dynamically generated model.
It works like this:

# ...
    # model_cls - динамически сгенерированная модель
    class ValidationForm(ModelForm):
        class Meta:
            model = model_cls
            fields = '__all__'
    form = ValidationForm(params)
    if form.is_valid():
        params = form.cleaned_data
    model_cls.objects.create(**params).save()
    # ...

With this approach, the language is taken into account and therefore the date of the form "09/04/2014" is processed without errors.
Now the task arose to save a separate value in a separate model:

function func(model_cls, row_id, field_name, field_value):
    row = model_cls.objects.get(id = row_id)
    row.__setattr__(field_name, field_value)
    row.save()

This approach does not work, because does not take into account the language and requires dates in the format "YYYY-MM-DD"
How to solve this problem in a more beautiful way?
UPD. It would be desirable to do standard validation with transformation, but not for the form, but only for one field.

Answer 1

Settled on this one:

# ...
    class ValidationForm(ModelForm):
        class Meta:
            model = model_cls
            fields = (field_name, )
    params = {field_name: field_value}
    form = ValidationForm(params)
    if form.is_valid():
        field_value = form.cleaned_data[field_name]
    # ...
    row = model_cls.objects.get(id = row_id)
    if hasattr(row, field_name):
        row.__setattr__(field_name, field_value)
        row.save()
# ...