TinyMCE broken after upgrade to 5.1.2

Hello everyone!

So i've updated plone from 5.1.1 to 5.1.2 and now TinyMCE doesn't load anymore.

Console displays this:

Uncaught TypeError: Cannot read property 'documentElement' of undefined
    at Th (plone-logged-in-compiled.min.js:1)
    at Sh (plone-logged-in-compiled.min.js:1)
    at hk.toggleNativeEvent (plone-logged-in-compiled.min.js:1)
    at toggleEvent (plone-logged-in-compiled.min.js:1)
    at bh.s [as on] (plone-logged-in-compiled.min.js:1)
    at hk.on (plone-logged-in-compiled.min.js:1)
    at ia (plone-logged-in-compiled.min.js:1)
    at Object.setup (plone-logged-in-compiled.min.js:1)
    at new <anonymous> (plone-logged-in-compiled.min.js:1)
    at UC (plone-logged-in-compiled.min.js:1)

I've noticed that this error only happens when changes are made to tinyMCE config, in my case I added the following code to Other Settings in the Advanced tab:

{
    "language": "pt_BR"
}

If I remove this configuration the editor loads just fine, except that everything goes back to English...
This also happens on a newly created plone site.

Does anyone have the same problem? Or have a clue on how to solve it?

Just realized there is a open ticket for this:

Plone Foundation Code of Conduct