First read, then comment: CommentCaVa disables the comment field for a certain amount of time. This time is calculated from the length of the blog post. Reading speed is set to 30 characters per second. Previous comments are not counted.
CommentCaVa is only a small JavaScript file that also runs outside of WordPress with minor modifications. The waiting message is currently displayed in English (default) or German, according to the browser settings.
This project was subject of my story about blog comments in c’t Magazin 17/2013.
Wishlist: * add more languages, maybe via WordPress plugin i18n * use WordPress options for settings (reading speed, waiting messages, locked comment styling)