formJsonLocalized(forcedOutputFormat = null) {
        return JSON.stringify(this.formArrayLocalized(forcedOutputFormat));
    }
Return a JSON string containing an object representing the form input values.
This is based on the result of the `formArrayLocalized()` function.

@param {null|string} forcedOutputFormat If set to something different from `null`, then this is used as an overriding outputFormat option
@returns {string}