I do not use the visual editor myself but just noted that this good-faith edit which was tagged as visual edit flooded an entire Wikipedia article with inappropriate <span dir="rtl" lang="ta">...</span> constructs.
Topic on VisualEditor/Feedback
User error (or user malice). He did "select all" and then chose Formatting -> Language -> Tamil from the menu.
I've seen that a couple of times before. I have always assumed that the user was hoping innocently for a translation of the article.
Perhaps it could be helpful if the visual editor would be more reluctant to update an entire page this way. The problem is that such updates are not immediately noticed and the fix causes quite some work if a series of regular edits follows. (In the example above the edit lasted for one and a half year until I fixed it.)