CodingFabian

Because WPML creates posts and pages for each language, comments from one do not appear on the other. 
This plugin merges comments from all WPML translations of the posts and pages, so that they all are displayed on each other. 
Comments are internally still attached to the post or page they were made on.
It uses the <code>get_comments()</code> api call, which in some circumstances might not return all posts.

WPML comment merging

This plugin merges comments from all WPML translations of the posts and pages, so that they all are displayed on each other.

Simon Wheatley

Jean

Ricky Poon

Because WPML creates posts and pages for each language, comments from one do not appear on the other.
This plugin merges comments from all WPML translations of the posts and pages, so that they all are displayed on each other. 
Comments are internally still attached to the post or page they were made on.
It uses the <code>get_comments()</code> api call, which in some circumstances might not return all posts.
This is a fixed version of the no longer maintained WPML Comment Merging plugin: 
<a href="https://wordpress.org/extend/plugins/wpml-comment-merging/" title="wpml-comment-merging" rel="ugc">https://wordpress.org/extend/plugins/wpml-comment-merging/</a>
Thanks to Simon Wheatley for contributing the fix.
Forked from: <a href="https://github.com/jgalea/wpml-comments-merging/" title="Github" rel="nofollow ugc">https://github.com/jgalea/wpml-comments-merging</a>

Merged Comments for WPML

An updated version of the fixed version of the no longer maintained WPML Comment Merging plugin.

WPML comment merging vs Merged Comments for WPML