It refers to the written language (e.g. English or German or whatever) rather than bad language.
When Communities are set up, the allowed languages are set up. Usually, people choose 'English' and 'Unspecified', meaning that posts/comments are accepted if they're explicitly tagged as English, or if there is no tag at all.
In Alexandrite, the default tag of English is chosen. If you're getting that Error when trying to post, it's typically because the Community has only been set up to allow 'Unspecified' - in which case, changing the drop-down from English to 'Undetermined' will allow you to post.