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.

jstar198

Adds an extra panel to the post/page edit page which allows you to enter the META keywords & description for that page in each enabled language. Also adds an optional browser title override (does not affect post title).
Note 1: This plugin requires that <a href="http://www.qianqin.de/qtranslate/" rel="nofollow ugc">qTranslate</a> is installed and activated.
Note 2: This plugin does not work well with <a href="https://wordpress.org/extend/plugins/all-in-one-seo-pack/" rel="ugc">All In One SEO</a> and potentially any other plugin or theme which tries to set your META tags.
<h4>Thanks</h4>
I’d like to thank the following people for their contributions (in chronological order):
<ul>
<li>Victor Berchet — Help with initial localisation; French translation</li>
<li>Benoit Gauthier — autosave bug fix</li>
<li>Filippo Pisano — Italian translation</li>
<li><a href="http://pc.de/" rel="nofollow ugc">Marcis G.</a> — Belorussian translation</li>
<li>Almaz — Russian translation</li>
<li><a href="http://www.heftrucknederland.nl/" rel="nofollow ugc">Renate Kramer</a> — German translation</li>
<li><a href="http://wpwebshop.com/blog/" rel="nofollow ugc">Rene</a> — Dutch translation</li>
<li>banane — Bugs with WordPress 3 compatability.</li>
<li>Alexander of <a href="http://webhostinggeeks.com/" rel="nofollow ugc">Web Hosting Geeks</a> — Romanian translation</li>
<li>Branco Radenovich of <a href="http://webhostingw.com/" rel="nofollow ugc">Web Hosting Watch</a> — Slovakian translation</li>
</ul>

qTranslate META

For users of qTranslate, allows you to set multi-lingual META tags and a <title> override for your posts and pages.

WPML comment merging vs qTranslate META