What is WPML?
Well, I think the best answer will be:
“WordPress plugin that allows you create multilingual content (posts, pages, custom post types and much more) under one CMS/admin dashboard”.
More information about this magic plugin you can find here WPML website.
What does it mean, WPML support?
It means, that you can configure plugin settings per language. For example, on English website you want to display underline links button, and on Russian website, you don’t want to display that button, so now you can do that! All WAH PRO options will be controlled by you per website language. Even more, you can translate all buttons strings without any .po or .mo files, simple as is. Put your text labels per website language.
And of course, you don’t have to enable this feature, if you want set plugin settings one time for all languages, and translate plugin strings with .po and .mo files, or with WPML string translation.
You will be able to see WMPL Support section only if you have WPML plugin installed, so if you can’t see it, that means, your WPML plugin is not activated or is not installed.