Magento – Upgrade TinyMCE to V4 on Magento 2

in this file magento_installation_directory/js/mage/adminhtml/wysiwyg/tiny_mce/setup.js, on line 97(Magento 1.7.0.2 CE) you will find a variable named settings. You need to add this option: entity_encoding : "raw". You can read more about it here tinymce.com/wiki.php/Configuration:entity_encoding. Please note that if you upgrade Magento, you may need to apply this again.

You can esily create your own module (depends on Mage_Adminhtml) which is extending that js file:

config.xml:

<?xml version="1.0"?>
<config>
    <modules>
        <Your_Module>
            <version>0.0.1</version>
        </Your_Module>
    </modules>

    <adminhtml>
        <layout>
            <updates>
                <your_module>
                    <file>your/module.xml</file>
                </your_module>
            </updates>
        </layout>
    </adminhtml>
</config>

In your layout file you add a custom js to the header:

<?xml version="1.0"?>
<layout>
    <default>
        <reference name="head">
            <action method="addItem">
                <type>skin_js</type>
                <name>your_module/wysiwyg/tiny_mce/setup.js</name>
                <params/>
                <if/>
                <condition>can_load_tiny_mce</condition>
            </action>
        </reference>
    </default>
</layout>

And in the new setup.js you can overwrite the prototype object:

(function (getSettings) {
    tinyMceWysiwygSetup.prototype.getSettings = function (mode) {
        var oSettings = getSettings.call(this, mode);
        oSettings.extended_valid_elements = "article[class]";
        return oSettings;
    };
}(tinyMceWysiwygSetup.prototype.getSettings));