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.

FreshFunBits

This small plugin removes any language content on your WPML site. This plugin works fine with all WPML versions since its idea is based on the <a href="https://wpml.org/documentation/support/wpml-tables/" rel="nofollow ugc">WPML’s Tables</a> official guide.
Features:
<ul>
<li>Remove the content of a specific language completely.</li>
<li>Have the option to choose <code>Items deleted per batch</code>, make sure your site will not be crashed.</li>
<li>Work independently with WPML.</li>
</ul>
You can report bugs or contribute code on <a href="https://github.com/FreshFunBits/ffb-delete-wpml-language-content" rel="nofollow ugc">this GitHub repo</a>.

Delete WPML Language Content by FreshFunBits

Remove any language content on your WPML site. It is useful when you no longer want the content of a specific language.

WPML comment merging vs Delete WPML Language Content by FreshFunBits