Django override default form error messages

The easiest way is to provide your set of default errors to the form field definition. Form fields can take a named argument for it. For example:

my_default_errors = {
    'required': 'This field is required',
    'invalid': 'Enter a valid value'
}

class MyForm(forms.Form):
    some_field = forms.CharField(error_messages=my_default_errors)
    ....