Changing the text directionality of TinyMCE impacts the whole interface

[Chouby]

On a multilingual site, it's possible that a writer has his interface in one language and writes posts in another language, possibly with a different text direction. For example, I can have the interface in English and need to write posts in Arabic. In that case I will want to change the text direction only in the editor.

With Gutenberg, changing the text directionality of Tiny MCE also impacts the text direction of the interface when I would expect it to change the text direction only in Tiny MCE.

Steps to reproduce the behavior:

1. Create a plugin with this code snippet:

add_filter( 'tiny_mce_before_init', function( $mce_init ) {
	$mce_init['directionality'] = 'rtl';
	return $mce_init;
} );

2. Edit a post with Gutenberg

Here is a screenshot with Gutenberg. The rtl text direction is unexpectedly applied everywhere:

Here is the screenshot with the classic editor. The rtl text direction is applied only to Tiny MCE as expected:

Related: #138

[ellatrix]

Huh.

[designsimply]

Tested and confirmed using WordPress 4.9.8 and Gutenberg 4.2.0-rc.1 that adding the following snippet (I cheated and added it to the bottom of an existing) plugin results in the whole interface getting affected after the classic block is added.

add_filter( 'tiny_mce_before_init', function( $mce_init ) {
	$mce_init['directionality'] = 'rtl';
	return $mce_init;
} );

^{Seen at http://alittletestblog.com/wp-admin/post.php?post=15501&action=edit running WordPress 4.9.8 and Gutenberg 4.2.0-rc.1 using Firefox 63.0 on macOS 10.13.6.}

Aside: I also spotted lots of 500 errors for API calls to autosave after making this change and adding a classic block:

{"code":"empty_content","message":"Content, title, and excerpt are empty.","data":null}

[jorgefilipecosta]

With the last version of WordPress and Gutenberg 5.8, the problem is still happening. The interface does not becomes in RTL right away but as soon as a classic block is added everything becomes RTL.

[paaljoachim]

Hi @Chouby and @designsimply
Can you please retest using the newest version of WordPress and Gutenberg plugin.
How can we move this issue onward?

[glendaviesnz]

With moving the classic block to a modal in block theme this is no longer a problem so closing.