ParsleyJS - Localization with data-parsley-`constraint`-message

Why don't you use the localization of Parsley instead of defining the messages on the inputs?

I suggest you download the localizations that you need from the source. After that, according to the docs you can load the i18n before the plugin, like this:

<script src="i18n/fr.js"></script>
<script src="i18n/it.js"></script>
<script src="parsley.min.js"></script>
<script type="text/javascript">
    window.ParsleyValidator.setLocale('fr');
</script>

Or you can load the i18n after the plugin (in that case, it will assume the last loaded localization - in the following example it will be Italian), like this:

<script src="parsley.min.js"></script>
<script src="i18n/fr.js"></script>
<script src="i18n/it.js"></script>

On my projects I typically load the needed localization based a Cookie or Session variable:

<script src="parsley.min.js"></script>
<script src="i18n/"<?= echo $lang ?>".js"></script>

With either of the options, you don't need to add data-parsley-constraint-message to each input. And when you need to change a message you can do that in the localization file.

To conclude, if you need custom validators, you can check the docs to see how you can define the different localizations.

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UPDATE

_{This solves the OP's need by changing the source code of the plugin}

You can edit in your parsley.js a method called _getErrorMessage (line 1264 with 2.0.4), which looks like this:

_getErrorMessage: function (fieldInstance, constraint) {
    var customConstraintErrorMessage = constraint.name + 'Message';
    if ('undefined' !== typeof fieldInstance.options[customConstraintErrorMessage])
        return window.ParsleyValidator.formatMessage(fieldInstance.options[customConstraintErrorMessage], constraint.requirements);
    return window.ParsleyValidator.getErrorMessage(constraint);
},

To something like this:

_getErrorMessage: function (fieldInstance, constraint) {
    //added
    var locale = window.ParsleyValidator.locale;
    var namespace = fieldInstance.options.namespace;
    var customConstraintErrorMessage = namespace  + constraint.name + '-' + locale;

    if (fieldInstance.$element.attr(customConstraintErrorMessage)) {
        // treat parameters
        if (fieldInstance.$element.attr(customConstraintErrorMessage).indexOf("%s") !== -1)
            return window.ParsleyValidator.formatMessage(fieldInstance.$element.attr(customConstraintErrorMessage), constraint.requirements);
        return fieldInstance.$element.attr(customConstraintErrorMessage);
    }

    // original
    var customConstraintErrorMessage = constraint.name + 'Message';
    if ('undefined' !== typeof fieldInstance.options[customConstraintErrorMessage])
        return window.ParsleyValidator.formatMessage(fieldInstance.options[customConstraintErrorMessage], constraint.requirements);
    return window.ParsleyValidator.getErrorMessage(constraint);
},

With this, you can specify the messages directly in the input, using the sintax data-parsley-constraint-locale. Here is a sample:

<input type="text" name="name" value="" data-parsley-required="true"
    data-parsley-required-en="Name is required"
    data-parsley-required-pt="O nome é obrigatório" />
<input type="number" name="phone" value=""
    data-parsley-minlength="9"
    data-parsley-minlength-en="Phone length must be equal to %s"
    data-parsley-minlength-pt="O telefone deverá ter %s digitos" />

When you need to use some kind of constrains (in the above example, there is data-parsley-minlength which is variable) you can use the %s inside the message. This will be replaced for the correct value.

Just before you bind parsley to your form, you need to set the locale you want to use (beware: you need to include the javascript file relative to the locale that you are using, otherwise you will get an error like Error: pt is not available in the catalog):

window.ParsleyValidator.setLocale('pt');
$("#myForm").parsley();

Here is a jsfiddle for demonstration. If you want to test, just setLocale('en') and see the messages in English.