WordFez is a plugin for bilingual (French-English) posts. It is seamlessly integrated into WordPress using a TinyMCE plugin.
It will add 2 extra buttons in the WYSIWYG interface for French and English language. Each button inserts 2 anchors to surround each language. The anchors are labeled by small flags. 
The usage is very straight-forward. The plugin comes with a widget to allow each reader to conveniently and instantly switch between the languages.
You need WordPress 2.5 at least.
New in v0.2.1:
<ul>
<li>Compatibility with WordPress 2.5</li>
<li>Fix a small problem in ‘alt’ fields</li>
</ul>

WordFez

WordFez is a plugin for bilingual (French-English) posts. It is seamlessly integrated into Wordpress using a TinyMCE plugin.

Jonathan Desrosiers

Linchpin

Aaron Ware

Note: This plugin does not support the block editor but should continue to work without issue when using it with custom post types and the <a href="https://wordpress.org/plugins/classic-editor/" rel="ugc">Classic Editor Plugin</a>.
Before WordPress displays a post’s content, the content gets passed through multiple filters to ensure that it safely appears how you enter it within the editor.
One of these filters is <a href="https://codex.wordpress.org/Function_Reference/wpautop" title="wpautop" rel="nofollow ugc">wpautop</a>, which replaces double line breaks with <code></code> tags, and single line breaks with <code> </code> tags. However, this filter sometimes causes issues when you are inputting a lot of HTML markup in the post editor.
This plugin displays a checkbox in the publish meta box of the post edit screen that disables the <a href="https://codex.wordpress.org/Function_Reference/wpautop" title="wpautop" rel="nofollow ugc">wpautop</a> filter for that post.
Also adds a ‘wpautop’, or ‘no-wpautop’ class to the post_class filter to help with CSS styling.

Toggle wpautop

Easily disable the default wpautop filter on a post by post basis.

WordFez vs Toggle wpautop