What happened?

Summary

Joomla's core client-side form validation reads a field's data-validation-text HTML attribute and uses its value verbatim as the "invalid" message:

media/system/js/fields/validate.es6.js, markInvalid():
const message = element.getAttribute('data-validation-text');

It only falls back to a translated string, Joomla.Text._('JLIB_FORM_FIELD_INVALID_VALUE'), when the attribute is absent entirely.

data-validation-text can be set per field directly from form XML, because
FormField::setup() copies every data-* XML attribute into $dataAttributes verbatim:

foreach ($this->element->attributes() as $key => $value) {
    if (str_starts_with($key, 'data-')) {
        $this->dataAttributes[$key] = $value;
    }
}

At no point in this chain (XML attribute → FormField::$dataAttributes → field layout → HTML attribute → validate.es6.js) does the value pass through Text::() / Joomla.Text.(). So an extension or template developer who — reasonably, given how label, description and hint behave elsewhere in form XML — sets data-validation-text="MYEXT_FIELD_INVALID_MESSAGE" will see the raw, untranslated language constant shown to end users as the validation error, in every language.

Steps to reproduce

1. Add data-validation-text="SOME_LANG_KEY" to any form field in a component's XML (e.g. a calendar or text field), where SOME_LANG_KEY is a defined language string in the extension's language file.
2. Trigger the field's client-side validation (e.g. a pattern mismatch or a required violation).
3. Observe: the invalid-feedback text shows the literal string SOME_LANG_KEY, not the translated text.

Expected behavior

Either:

• Document that data-validation-text must contain literal, pre-resolved text (not a language key), so developers don't assume it behaves like label/description/hint; or
• Resolve data-validation-text (and similarly end-user-facing data-* attributes) throughText::_() when building dataAttributes, consistent with how label/description/hint are already translated in form XML.

Environment

Verified against the current source on both active branches:

• 5.4-dev (repository default branch) — build/media_source/system/js/fields/validate.es6.js
• 6.1-dev (current 6.x branch; 6.2-dev does not exist yet) — same file, identical logic

Same element.getAttribute('data-validation-text') / no Text._() call in both.

Version

5.4

Expected result

No response

Actual result

No response

System Information

No response

Additional Comments

No response