Magento :: Translate text from javascript files

Just use the following method in your scripts:

Translator.translate('Some phrase');

You can do it in a template file yourfile.phtml. The JavaScript js/mage/translate.js file must be included in your HTML header (Magento does it by default).

<script type="text/javascript">
    Translator.add('You should take care of this confirmation message!','<?php echo Mage::helper('yourmodule')->__('You should take care of this confirmation message!')?>');
</script>

Since Magento 1.7, you can add a file jstranslator.xml into your module under the etc/ folder and set the following string like that:

<jstranslator>
    <!-- validation.js -->
    <validate-no-html-tags translate="message" module="core">
        <message>HTML tags are not allowed</message>
    </validate-no-html-tags>
    <validate-select translate="message" module="core">
        <message>Please select an option.</message>
    </validate-select>
</jstranslator>

Then translate the string as you do it for PHP thanks to the CSV file. This will add the translation to the JavaScript code like the following var Translator = new Translate(...).