$l_anonymous variable should be defined in all of your language packs. For examle, if you have language packs A and B, then in A, it will be defined as:
(translated of course to the necessary language). Then you should define:
...etc. But this is just for preventing registering users under "anonymous" name, so you don't see on the board "Anonymous" nickname amongst "Anonymous" membername. Additionally, if your language pack uses symbols other than latin, and users can not use these symbols in their reg.names, then you don't need to define it.
If your board is open only for registered members, you don't need to define it - or just define unwanted nicknames then.