In rtl based communities the direction of forms are right to left, This direction change causes lot of BBCode related problems for users of rtl languages, as example screenshot this BBCode phrase contains persian alphabet, persian words between tags change standard phrase of BBCodes (place of slashes) therefore users find BBCode so difficult and hard to read, link to texts, etc
related discussion topic : http://area51.phpbb.com/phpBB/viewtopic.php?f=81&t=43017