Support overriding RECAPTCHA_ERROR_CODES

[PanderMusubi]

The recaptcha error codes are in English, see https://github.com/wtforms/flask-wtf/blob/main/src/flask_wtf/recaptcha/validators.py#L10 and I would to overrride them with my (Dutch) translation.

    app.config['RECAPTCHA_ERROR_CODES'] = {
        'missing-input-secret': 'De geheime parameter ontbreekt.',
        'invalid-input-secret': 'De geheime parameter is ongeldig of misvormd.',
        'missing-input-response': 'De responsparameter ontbreekt.',
        'invalid-input-response': 'De responsparameter is ongeldig of misvormd.',
    }

Even better would be that translations (via existing gettext i18n?) for all supported languages are shipped with Flask WTF. Like with content of the widget, the browser's locale is used, but can also be overridden with:

    app.config['RECAPTCHA_PARAMETERS'] = {'hl': 'nl'}

It should work for recaptcha and hcaptcha. But overriding with a dict as shown above would be a good first step.

See also #583

[PanderMusubi]

Oops, duplicate of #198