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.

Seisuke Kuraishi

Multibyte functionality enhancement for the WordPress Japanese package. 
<a href="https://eastcoder.com/code/wp-multibyte-patch/" title="Documentation in Japanese" rel="nofollow ugc">日本語の説明を読む</a>

WP Multibyte Patch

Great!

いつも大変お世話になってます！ありがとうございます！

Thanks You!

Great plugin

Multibyte functionality enhancement for the WordPress Japanese package.

WPML comment merging vs WP Multibyte Patch