When you need a free plugin that would make your WordPress site multilingual, qTranslate-X is a way to go. It works great, but you might encounter a problem when trying to have multiple language support for attributes of Featured Image also known as Post Thumbnails. If you try to insert qTranslate language tags in Title, Description, Caption, and most importantly Alternative Text, you might notice that nothing gets translated when
the_post_thumbnail() is called.
This article will show you how to make those fields multilingual.