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.

OzTheGreat

Adds a multiple select box to every non-admin user profile that allows admins to 
select which languages that user can see / edit in the wp-admin.
Languages that a user cannot see are hidden. If they try to switch surreptitiously 
it will throw an error message.
This plugin REQUIRES WPML and is useless without it.

WPML Editor Languages

Allows admins to restrict users to specific languages in the WordPress admin

WPML comment merging vs WPML Editor Languages